Grain door status monitor

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wllshaw

Member
Newbie question here. I have been reading the manuals, forums, FAQ's, and past threads since Christmas. I have decided on my first project, but I need a bit of advice. The project involves monitoring the status of a door located at the bottom of a grain cart that is used to move grain out of a field and to a dump pit. It is removed from the bottom of the wagon by the door in question. After the grain has emptied out of the wagon, it is returned to the field to be filled up again. If the operator is not doing his job, he can return to the field with the bottom door still open. The next load of grain is then emptied into a wagon with an open bottom, and a HUGE mess ensues. I am the person who gets the opportunity to clean these messes up. Hence my idea.
What I would like to do is use the 18x picaxe I have, to monitor this door and turn on either a green or a red LED and sound a buzzer. It is about 5 meters from the door in the wagon to the tractor cab where the 18x and LEDs will be located. The picaxe will be powered by a 12V batter that provides the tractor with power. Obviously that voltage will have to be cut down. However, my question involves the door. What type of sensor or switch would you guys suggest I use to monitor the status of the door. With a distance of 5 meters I can have a physical wire connect the picaxe to the sensor. Since I am a newbie, I prefer to keep this relatively basic and within my ability. The programming I believe I can handle. There are plenty of examples in the manuels utilizing buzzers and LEDs.
Any suggestions would be appreciated.

Will
PS: Thanks Hippy for the answer to my LDR question. It worked great.
 
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papaof2

Senior Member
What material are the wagon and door made of?

If they are non-magnetic, then a magnetic reed switch and a magnet are ideal beause the contacts are sealed inside a glass tube and can't get dirty.

If the materials are steel or similar material, then a microswitch mounted at the hinge side might be a good choice (again, an enclosed switch).

The PICAXE might be overkill here, as the switch and a couple of resistors could drive the red and green LEDS directly from 12 volts and reduce the total number of parts required (thus reducing the likelihood of failure).

John
 
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BCJKiwi

Senior Member
The sensor will need to be sealed against water and dust and be a changeover contact type to give positive feed back on both door open and closed.
Then No LED = wiring open circuit.
Short circuit???

Would suggest one of the industrial type 4 wire inductive proximity switches which are fully sealed and can take a lot of punishment.

Something like this (there are many manufacturers and variations on voltage, mounting, sensing range etc including shielded types that cope with surrounding metal).
http://www.am.pepperl-fuchs.com/products/product.jsp?product_id=15650
 
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BrendanP

Senior Member
Get these sensors from Mouser in Texas P/N. 540-MP201903. Sealed for life, have mounting points, will last forever. When the magnet is close to them there closed and so the LED will be on. Theres a variety of magnets to go with them with different mounting set ups.

So when the grain door is closed the light will be on, if the light is off the grain door is open. You dont need the picaxe for this app. Get some cable and cable ties to attach it to the machine as well. Get a voltage reg from Mouser with the sensor. Use the P/N 512-KA378R33TU. This will give you 3.3 V out to run the LED off the combine/tractor/trucks power supply.

Its a simple project, a picaxe could handle more complex matters. Engine management on a irrigation pump maybe.

As papa says maybe just use some R's rather than the V reg.
 
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wllshaw

Member
John: The wagons are made of steel, and I do realize that I am over killing this project by involving a PICAXE. :) It's just that I have a need for this device, and I thought it would be a great way to learn about voltage regulators, gathering input from sensors, making a simple PC board, incorporating the simple programming, and ending up with something I really needed. I realize it would not be cost effective, but I thought it would be a nice second step after having completed the exercises in the manuals. I also thought it would be a great learning opportunity. The last time the door wasn't closed I had 200 bu. of corn spread out over 1/2 mile. At todays price of $5.00/ bu, you can see I can spend some money here and still be ahead in the game. Also I just don't have the heart to tell my father that he is too old to work on the farm he built.
In regards to the rest of the forums advice, many thanks. The sealed swithces look great. I'll check into them and get back to you.
PS: Project number 2 involves control of a wind generator that I have already built. But I am following the advice of previous posts on a similar subject and starting with smaller ideas i.e. grain door sensors.
Many thanks.
Will
 
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BrendanP

Senior Member
My experience suggests get the simple version going and then add compelexity latter if you so choose.
 
hippy

hippy

Technical Support
Staff member
A magnetic reed relay should work regardless of the steel construction. As suggested, get the switch working first then add a PICAXE.

Although a PICAXE isn't absolutely necessary it can be used to add a delay between opening the grain door and the audible "not closed" alarm going off. That will help avoid it becoming a stress source and your eventual discovery that someone has taken a hammer to it out of annoyance.
 
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papaof2

Senior Member
A PICAXE could be interfaced to a strain gauge to detect the weight difference between loaded and unloaded and whether the wagon is being loaded or unloaded.

If the weight is greater than the unloaded weight and the door is open, then you have one of two states:
1. load in progress (weight increasing) - need audible alert
2. unload in progress (weight decreasing) - only need visual alert

To detect the case where the door comes open in transit, the audible alert should always operate for a couple of seconds on the opening of the door. Or you can add a motion detector that uses a light and photosensor aimed at a reflective (white paint?) spot on one of the tires. If in motion and the door comes open, make a really annoying noise ;-)

You can buy a "real" strain gauge and the associated electronics or you can experiment with a variable resistor (potentiometer or pot) with an arm on the shaft that is attached to some part of the wagon that moves down (in relation to the axle) when the wagon is loaded. The pot needs to be protected from water and dirt, but a simple box with a rubber gasket around the shaft of the pot may suffice.

Read the value of the pot with the PICAXE's ADC to determine how much load there is. You won't get to-the-bushel accuracy, but might get measureable changes with 50 bushels or so (I haven't seen your wagon, so this is based on other farm wagons I have seen). An unsprung wagon will have some give in the metal as the load increases. A wagon with spring suspension will have some compression of the springs. You'll need to do a lot of experimenting ;-)

John
 
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Dippy

Moderator
"A PICAXE could be interfaced to a strain gauge to detect the weight difference between loaded and unloaded and whether the wagon is being loaded or unloaded."
- couldn't the driver just turn his head ? :)
 
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steliosm

Senior Member
I would also like the idea of a reed switch connected to a 08M and the 08M connected to a wireless Tx modules. This module will transmit for example the id of the wagon and the door status. Another PICAXE which you could have on you will be connected to a Rx module to receive status messages of the modules in range.
You might need to read a bit more, but you could end up with a nice little system to monitor what you need.
 
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papaof2

Senior Member
He wants to use the PICAXE for more things, so weight sensing and the direction of weight change are "more things".

Since the driver in the original post drove off with the wagon loaded and the door open, the status of door open/closed plus the status of loading/unloading might be of value ;-)

John
 
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BrendanP

Senior Member
Remember, KISS.

The part I recommended from Mouser is a hall effect sensor, I dont think it will be affected by steel near it??

Remember, KISS.
 
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wllshaw

Member
Power supplys for the grain door monitor

I tooke BrendanP's advice and got the sensors from Mouser. Nice looking sensors that look like they will do well in the enviroment they will operate in. I have them connected to a breadboard with an 18X and have my program running. The 18x is driven off of a 4.5V battery pack. I believe I am now ready to convert the 18x to run on a 12V system supplied by the tractor. I checked some of the old posts and I believe I need to run a voltage regulator to the 18x. The posts I looked at suggested a 7805A voltage regulator. They came from 2004 though, so my questions is this. Will the 7805A work well for me, or is there something better out there? I plan on adding a transistor to power a bigger 12 V light in the future and also a piezo sounder to give me a audible alarm. Am I on the right track or does the forum have any better suggestions.
I have posted the code I have so far. I pasted it here so it doesn't look the best. I am still working on how the pro's make their code look so nice. Feel free to offer any suggestions that make it more effecient.
CODE
main:
if pin1=1 then goto light " Monitors pin1 for door opening
goto main

light:
let b0 = 0 'Sets b0 to zero
for b0= 1 to 20 'Starts unloading delay
pause 70 'Debounce switch
high 4 'Turns on Red LED
pause 50 'Delay
low 4 'Shuts of Red LED
pause 50 'Delay

if pin1 = 0 then goto main 'Test for premature door closing.
next b0 'returns to top or For Next Lo
'Drops prog into buzz

buzz: 'Code that turns buzz and light on at end of wagon unload

high 4 'Red LED on
high 5 'Pin5 on with transistor driving buzzer
pause 50 'Delay
low 4 'Shuts off Red LED
low 5 'Shuts off pin5 transistor driving buzzer
if pin1=0 then goto main 'Test for door closing. Returns to main to monitor door
if pin1=1 then goto buzz
end

Many thanks
Will
 
lbenson

lbenson

Senior Member
Re your regulator, the 7805 is very power hungry, and not recommended for AA battery operation. Tom2000 in this thread -- http://www.picaxeforum.co.uk/showthread.php?t=8539&highlight=L4941 -- and in another one which I can't find pointed out the TI L4941 LDO "7805 drop-in replacement". For currents below 100ma, the LM2931 looks good. Both of these have tighter-than-normal capacitor requirements--as Dippy would say, check out the data sheets--for "drop-out voltage" and "quiescent current" in particular in this case, and the recommended circuits. Depends upon your needs. If you run off the tractor battery the drain of the 7805 may not be too much of a problem, but cautions regarding amending your tractor's electical system might be in order (tho you don't have quite the safety concerns as with an automobile on the public highways). Separate power in your case might make your life simpler.
 
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BrendanP

Senior Member
Mouser also have a large range of LDO V regs. I use a Fairchild part good for 3 amps comes in 3.3 and 5 V has a enable/disable pin as well.

Anything you get from Mouser is top shelf stuff. Its all "milspec/industrial strenght" sort of stuff. They aren't a amatuer hour supplier. Ask them for a copy of their paper catalogue.

As you get more skilled have a look at their range of vibration sensors and look into mouting them on pulley shafts bearing housings or engine mounts so as to give warning of bearing failure, engine mount failure and so on.

Have you got a few bread boards? That way you dont have to pull appart a existing project to do another or try a variation. Have you got a bench top power supply? Bread board all your designs and see how they work. A power supply with current limiting and digital read out of current consumption is a must have I believe.

As you become more skilled/confident you will find many apps on the farm for MCU based projects that will make jobs easier and the farm more profitable.
 
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Dippy

Moderator
Check out the Data Sheets - well you were told I'd say it :)

Not sure whether IBenson did a typo, but for <50mA battery stuff I'd suggest looking at the LM2936 as it is micropower. http://cache.national.com/ds/LM/LM2936.pdf

For <100mA check out LP2950 which comes in 3.0, 3.3 and 5.0V variants - also very good dropout and quiescent figures. http://www.farnell.com/datasheets/86217.pdf

(And the TI ones in Farnell are only 30p for one offs)

For battery power low power stuff always send the 7805 back to the Natural History Museum with the rest of the Dinosaurs.
However, if your you're using a power source with a large capacity (mains or vehicle) then it's fine, with spikesuppresion caveats.
DATA SHEETS - read, absorb and learn.

Vehicle Supply: Before the Gloom'n'Doom merchants swagger in with tales of death, just remember to provide fuse and suppressor before the regulator. 12--Fuse--Suppressor--Regulator--PICAXE. And any inputs should be 'scopd for transients too.

Vehicles can produce some nasty spikes though I have NEVER measured anything like the claims. But always build for the worst case scenario i.e. a nasty failure of some other part of the vehicle electrics. A simple LCR type suppressor will be fine and maybe chuck in a transient type for good measure. And a 1 to 3 amp in-line fuse before your suppressor/regulator/PICAXE would be a good idea.
In this vehicular case, forget dropout and quiescent current figures. Just make sure that the Input voltage is 30V at least, so it can take a bit of a transient post suppressor. HF spikes can go through a regulator like it wasn't there and can cause a PIC to fail or latchup.

And a screened enclosure would be a good idea.

Suppression isn't magic. The components used aren't unique to Mysterious Magicians working in the Giant Companies. They aren't made by Harry Potter. So, pinch a good suppression design and use Quality components of the correct rating.

Obviously your circuit will be firmly fixed into a protective enclosure and it will have been thoroughly bench-tested. It will not be a hairy bread-board stuffed into a biscuit tin. It will not rely on Elastoplast to provide insulation or cable strain-relief.

But sadly, you've made the fatal juxtaposition of words in your posts :) i.e. PICAXE+Vehicle+Newbie. There will now follow 20 posts of warnings of death, famine and Global Warming.

Sorry about the length. I've drivelled on for longer than hippy normaly does.
 
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wllshaw

Member
Brendanp:
Vibration sensors, now I'm all aquiver. I didn't realize those were available. They are definately on my next project idea list. In regards to bread boards, yes, I have two right now, and am working the circuit out so it works flawlessly first. Then I'll move on to learning how to make a PC board. I have already read up on it. It is just a matter of giving it a try and evaluating the results. After a hopefully successful completion of the PC board I will mount it in a water proof container and then give it a test in actual conditions. I still have 7 months before harvest gets here to finish this project up. As far as a bench top power supply. No, at this time I am keeping the local convience store in business by purchasing their AA batteries. I'll take any suggestions on make and models of bench top supplys if you would care to make them. I am interested in the PICAXE for the farm and also for my other job. I am the Industrial Arts teacher at the local high school. My main area is in woodworking, but I thought I might branch out into electronics. It is a small school and there are no electronics classes offered. I thought I would at least take a few class periods and introduce the kids to the PICAXE system. While I obviously am not an electronics teacher, I wanted to at least expose the kids to the world of electronics. Hopefully, you may see one or two here on the forum in the future. Many thanks!

Dippy:
A newbie comment here. I was looking at the 7805 data sheet trying to figure out what all the info meant. Please correct me if I am wrong, but I am assuming the supression you are talking about is the capacitors that are located before and after the regulator. I am also assuming that these will trap spikes and smooth out the voltage being supplied to the regulator. I was looking at the 7805 because I happen to have one available, it's Easter, and Radio Shack is closed. In regards to Vehicle Supply. The newer John Deere tractors supply a power strip that is already fused. It provides power to the multitude of computers that now make up the inside of most tractors in America. Planting monitors, GPS systems, Autosteer, Sprayer monitors. The list goes on adnauseum. I will check to make sure of this statement, but I believe it is well isolated from the main vehicles electronics. If something fails, the fuse is blown, and you loose all your monitors. Trust me on this one. I have already done it while installing an autosteer. The fuse works great! Your electronics are dead but the vehicle continues to work as expected. In regards to enclosures, yes, I plan on making this look pro. There is nothing worse than having someone say "Did you make that"? It is much more satisfying to hear the statement "Where did you buy that?" I guess that means I'll have to throw the DucTape out. Darn. Please note the sarcasm. I'll take a look at the parts you suggested and get back to you guys here if I have any questions. Many thanks to all
Will
 
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Dippy

Moderator
Ah well, I'm the 'Newbie' as far as Tractors are concerned. I guess that power strip includes all the 'mystic' suppression required? Is there a Data/Spec sheet? Is it 12V output? (Can you test it and/or 'scope it for spikes?)

Regulators: No those capacitors are 'bypass' capacitors to provide stability to the regulator. And you should stick to (approx anyway) the values and types described in your device Data Sheet.

Any suppression is 'upstream' and would be in addition to those caps.

Even if your Power Strip contains active/passive suppressors I would still stick a small in-line fuse and 'car audio' type suppressor with your device and maybe a protection diode (i.e. so if you plug it in the wrong way round it doesn't blow up). And I would def have a couple of caps right next to the PICAXE power pins - maybe a 47uF and a small ceramic in parallel. This combo is recommended in many PIC data sheets.

Data Sheets again... there's no escape.
 
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BrendanP

Senior Member
I found the power supplies current read out very handy because it gives me a idea whats going on. You also want a supply that allows you to limit the current flow. You set the current limit before you power up the project, at oleast for the first time. I figure out what the max. is the project should draw and then set the power supply at that. Its saved me a few times when I've made wiring mistakes on bread boards. So In my view you want a power supply with current limiting, variable voltage regulation and digital read out of both. Just how many amps you need will depend on the projects you plan to work with.

Im not sure of a specific supply. I built mine from a kit. I learnt a bit doing so but theyre preety cheap to buy so it might not be worth while.

A CRO is a very handy thing to have as well.

You might feel as a beginner it isnt worth while having these tools in the beginning. I think it is as they make the job much easier.

PCB etching is easy. I've used the blue film iron on material with a lot of success. Use plenty of shoulder weight on the iron. Get a dremel tool and the stand that holds it vertically like a little drill press to drill out the holes.

Manuka, who posts regularly here has a lot of experience teaching picaxe. Hes in NZ. You could email him and set it up to give him a call, he could give you a lot of advice about teaching kids picaxe.
 
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Dippy

Moderator
I second the bit about PSUs and 'scopes.

I use a couple of different PSUs. One is a TTi (Thurlby Thandar, funny name). Superb quality. The other thing is an ancient old 60's UK made thing 'recycled' from the Admiralty skip ten years ago. Both are quality non-anonymous-cheap-Chinese products. You get what you pay for and they are totally reliable and with TTi you can speak in English to the manufs.

As a result of current limit control I don't pop prototypes.

Should be standard issue for projecteers and Students.

Brendan says CRO. That's the old-boys term for Oscilloscope.
And I really don't know how so many projecteers can do without a 'scope. Well, I can actually - they just flatter others into doing it for them.
Get a good one. Get one better than you think you'll ever need. Get a digital one. I enjoy spending your money, but you won't regret it - even if you have to go without coffee for the next month. Spend the extra and get a proper make.

I hope you realise that mentioning Manuka is like summoning a genie. Puff!- several pictures of breadboards will appear as if by magic :)

.
 
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wllshaw

Member
Dippy:
In the beginning I found my self having two windows open. One open to google and the other one on the forum. That way I could decipher what a CRO or a LDO V regulator was. In the beginning I even figured out what RTFM meant. By the way, it is googleable,---shame on you :) In regards to CRO's. When I first read the forum about silly scopes, visions of the 1950's CRT scopes came to mind. Then I did a google search and found you could plug these things into computers nowdays and set the whole thing on an envelope. Are these the norm for the present day or do you need to find one of the dino's from the past? I appreciate your comment about quality. I have found that it is best to buy the best pay once and then use the product for a loooooong time. If I may ask. What price range would you consider cheap? In other words, what should I stay away from? Regarding the PSUs. I will look into that when I get a byte. I mean bit. I am currently moving all my stuff off of the kitchen table. I have been relegated to the basement for some unforseen reason.

Thanks
Will
 
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BrendanP

Senior Member
Saying CRO makes me feel like I know what I'm talking about. I don't really, Ive only scratched the surface with the thing. But I wouldnt work without it now.

Mines the old style non pc type.

I think any PSU or 'scope made in a western country or Japan would be OK quality wise. Price is going to give you a good indication, pay peanuts- get monkeys.
 
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Dippy

Moderator
Personally I prefer the 'CRO' in a separate box, though I tried a PICO several years ago and was quite impressed.
I use Tektronix and have found them to be totally reliable. But you'll have to open that wallet pretty wide. There are also some Tektonix lookalikes which have lower specs. The new Tektronix have FFT functions too.

There are numerous manufs out there and I don't want to poo-poo any of them as I simply don't know.

On paper, the Digimess DS25 (another Chinese Tektronix lookalike) looks good value.
Mind you the Tektronix Accountants have been busy as (at least some if not all) Tektronix are now made in China.
The scope use the most is a Tektronix digital LCD and has been 100% and is 10 years old. Made in USA. It's been back a couple of times for re-cal. Try that with an Ebay special!

My criteria would be:-
A) Known manufaturer that is contactable.
B) At least 1Gs/s effective sampling rate.
C) Digital storage.
D) Option for calibration (you may not need it but it implies that it is adjustable which you won't get from a £100 Beijing Banger)
E) Once in a blue-moon FFT.

If you can afford it go for colour display. When you are using multi-channel and the lines all sit on top of each other then colour makes life easier.

For 'scopes, to name but a few, check out: Tektonix, Agilent, GW Instek, Metrix and if your wallet is bursting Lecroy.
For hand-helds check out Fluke.
PC-Based: Pico and if on a budget then chek Vellman.

Tektronix start with this model: http://uk.farnell.com/1225084/test-equipment/product.us0?sku=TEKTRONIX-TDS1002B

Bench PSUs. I look for 'proper makes', reliability, quality and, ideally, being able to contact manufacturer in my native language. I want to be able to leave that PSU working for several days and have the conficdence it ain't going up in smoke, hence TTi.

Check out: TTi(Thurlby Thandar) / Hameg / Digimess / Grundig. But there are quite a lot more. My pref is TTi as their factory is just up the road and if my PSU conked out I could throw it through their window.

PS. I have no commercial links to any of the manufs or Farnel/RS etc. It's just that Farnll/RS give really good warranty support - and no supplier in their right mind will give that level of support on second-rate products. Ebay? Pah!

PPS. There will now follow the 'My Favourite scope' list, followed by the 'Look what I got for a tenner off Ebay', followed by ' That Ebay one was great value but how can I trust the numbers it gives out' :)

Buy the Best, you won't regret it.
 
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BrendanP

Senior Member
Mouser carry a range of PSU and 'scopes.

Just leafing through their paper catalogue now, theres hours of geek/pencil neck/poindexter reading heaven there.

Man theres some nice gear in that puppy.
 
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Dippy

Moderator
Hey Brendan, tell me of a big-brand 'scope made in a western country. Lecroy is made in Japan.

Anyway, good luck Willshaw. Just remember, open that wallet...
 
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BrendanP

Senior Member
I don't know Dippy, I was just applying what I know of power tools, if it isn't metabo, hitachi, dewalt etc. I don't buy it.

Some of them are probabaly made in china too now but at least they will have western/japanese Q control in the plant rather than the local communist party/army hack who getting kick backs from the plant management to look the other way.
 
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papaof2

Senior Member
Bench power supply -
I have an ancient HeathKit (with analog meters) that's rated to provide up to 50 volts at 1.5 amps. There's a little voltage drift with heating, but a change of 0.1 volts at 18 volts over 4 hours isn't critical for the circuits I build (each board has its own regulator). I often leave it on for days at a time, knowing that it is properly fused, etc.

I have digital meters to add for voltage and current, but that the priority on that project is below installing additional rain barrels for my wife's flowers ;-)

John
http://www.wizardanswers.com/rain
 
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BrendanP

Senior Member
" I was think of fitting something to my wife's barrels".
Hey Dippy are you related to the late Benny Hill ?
 
hippy

hippy

Technical Support
Staff member
As a slight counter to what Dippy says on scopes, my advice is don't over do it. Spending hundreds or thousands on a scope which isn't going to get used will take money away from what could be far more usefully used elsewhere.

I've got by for the most part without a scope but acknowledge that they are useful and necessary in some cases. It boils down to what you're doing. I'd never buy an analogue scope ( unless bargain basement price second-hand ) because that doesn't suit what I do and nor do I normally need super-high bandwidth or sample rates.

With a bottomless wallet, or working professionally, buy the best there is, but for everyone else it's difficult to decide how much to spend. Under-spending can be just as pointless as over-spending, but the rule that you get what you pay for usually applies. Well known and recommended brand names have their reputations for a reason.

One thing I'll definitely agree with Dippy on is, that if you cannot trust your scope, then what use is it ? If you just want to see voltage levels going up or down anything from a dumpster skip or from the Ark which works will do, but time or accurate measurement requires something which is reliable.

The questions to ask are, "Why do I need a scope?", and "What must it do?"
 
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Dippy

Moderator
I wasn't really suggesting overdoing it to a mad degree, like spending thousands, that's daft, sorry.

"The questions to ask are, "Why do I need a scope?", and "What must it do?"
- True, but it should go a little further.

Assuming your interest in electronics is long-term serious (and isn't a five-minute-wonder) the question you really also have to ask is "What must it do to still be useful in 12 months time?".

Pointless spending £400 on a non-storage just to save, say, £150. 'Cos next year when you need a storage scope then you'll have to spend £550.

If you don't envisage a semi-long-term interest in electronics then forget it. My comments are for people in it for the long term and taking it seriously as a hobby or semi-pro.

If you just want to see if Serout is working then get a cheapie. If it's just a toy to show off to your friends then get some cheap anonymous brand off Ebay by all means.

A 'scope is an instrument, not just to show pretty pictures. An instrument must be trusted and therefore should really be sourced from a reliable manufacturer.
If you want it to make accurate and meaningful measurements then you'll have to part with the cash and get a 'famous make'.
(For real serious professional stuff you'll have to have it calibrated and certified. And only the 'proper makes' are good enough to justify this extra expense.)

But, if you're still at school and just doing electronics for exams, please don't hassle your parents for a really expensive one. Just use the nice ones at school that we taxpayers bought for you.


£600 will buy a good 'scope that should last years and be reliable and accurate and , above all, trustable (if there is such a word). And have a meaningful warranty.

.... and a 'proper' make will have a better second-hand value if needs be.
 
hippy

hippy

Technical Support
Staff member
Dippy said:
But, if you're still at school and just doing electronics for exams, please don't hassle your parents for a really expensive one. Just use the nice ones at school that we taxpayers bought for you.
Click to expand...
It's a real shame that there aren't more 'community resources' for people who don't have access to what they need. That extends well beyond electronics and into many fields, beyond schools and colleges. That 'co-operative, shared resource' culture should certainly pay back considering how many sewing machines, forty-foot ladders, and who knows what else, is laying idle for a lot of the time.

There are a few LETTS schemes ( Local Exchange and Time-Trading Schemes ) around, but they don't seem to be that well promoted nor coordinated. With all the talk of saving scarce resources, minimising waste and promoting sustainability it's disappointing that more isn't being done by national and local government to encourage them and provide funding to get them up and keep them running.
 
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Dippy

Moderator
Yes, that would be nice. I would have loved that type of thing years ago. It certainly would prevent a large number of 'white elephants'. My first CRO was an analogue storage Telequipment bought (legally) from UKAEA for a fiver, vintage 1803.
 
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BeanieBots

Moderator
For many years (and even now when I can't be bothered to dig out the 'scope) I got by with no more than an LED, resistor and loud speaker:)
Even a simple ripple counter and a stopwatch can go a long way towards saving the need for accurate timing equipment.
 
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eclectic

Moderator
User Project ideas.

BeanieBots.

It would be great if you could present these ideas in the Finished Projects Forum.

A circuit diagram and a quick explanation could be extremely valuable to newbies
of all ages and abilities.

e.
 
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BeanieBots

Moderator
eclectic said:
BeanieBots.

It would be great if you could present these ideas in the Finished Projects Forum.

A circuit diagram and a quick explanation could be extremely valuable to newbies
of all ages and abilities.

e.
Click to expand...
Umm.. Not enough to it to make a circuit worth drawing.
The resistor limits current, the LED lights (or not) depending on logic level.
If the LED is faint, either move it rapidly (Dippy's POV 'scope) or replace it with a load speaker. With practice, the ear is quite good at percieving square vs sine and frequency.
A bi-colour LED would give even more information.
 
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