Picaxe diy sensors ?

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curry87

Senior Member
How many kinds of sensors could be constructed fairly easily with the bare minimal components needed and still be fairly accurate without buying a self contained module off the self that does it for you ?

Is a homemade vibration sensor possible without using piezo + op amp method that is sensitive to detect near footsteps a few meters away for example ?

What other sensors are possible for use in a diy burglar alarm sensor network that could detect human beings but can be constructed with the least parts and construction time ?


Regarding constructing touch sensors and the new touch functions on the new m2 picaxes is it basically 2 wires one ground one from picaxe input with a insulated plastic on top ?
 
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Dippy

Moderator
Many years ago I made some step-mounted vibration sensors using those disc piezo ceramic devices from Maplin etc.
(Those thin brass-looking discs with the white piezo ceramic in the middle and 2 wires.)
Worked really well.

How far away something can sense will vary hugely depending on where it's mounted (i.e. the matrial and thickness etc) .
You can imagine how vibration is 'conducted'? And how far it can travel.
Vibration (low fq) could go miles on a trampoline and hardly any distance on 6" of reinforced concrete.

One home-made sensor that worked really well on a step was using the capacitive QProx senors.
The electrodes were interleaved 'fingers' of foil on a plastic plate.
Worked really well, except rain cause false triggers.

And that's another thing of course.
You make it super sensitive and you may suffer false triggers.
You need to ensure that the actual signal generated is oomphy.
For a weak o/p transducer you'll usually need more 'gain' , and the more GAIN = (usually) more PROBLEMS.

Have a long think about your requirements.
And do look around for sensors. There are some SO cheap that it isn't worth spending an hour trying to make one.
And let's be honest; in many cases the Big Boys can make something far better than you or I can.
 
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Rickharris

Senior Member
Vibration sensor - VERY sensitive, -break open a Zinc battery & remove the carbon rod. Drill small hole in centre across the Dia to take a pin for a balance. balance on 2 upright Stanly craft knife blades edge up on a thin board or box.

Get the rod to balance with slight bias to one end - You can put a collar of foil round the rod and slide to perfect the pressure.

Rest the end on another conductive surface - a brass drawing pin is good. Connection to rod and drawing pin results in 1. a VERY sensitive vibration switch, 2. a very sensitive carbon microphone.

Pressure sensor - Rigid container Balloon stretched across the top Glue a washer or coin in the centre of the balloon and use it to operate a microswitch, mechanical arrangement to suite what you have.

Tough switches = 2 drawing pins 1 in window frame and 1 on window break cct when window open.

With new 18M capacitive sensors are easy(ier)

Rather cruder vibration sensor/acceleration sensor is a piano wire mounted vertically attached at 1 end with some solder melted to the other end for a weight - Put the wire inside a copper tube connect between tube and wire. Longer wire give more sensitivity.
Light sensor - File the top off a transistor or if you junk box is as old as mine scrape the black paint off

you can detect movement and to some degree measure it by putting an LED at one end of a rubber tube and a photo transistor at the other stretching the tube cause it to occlude some of the light.

You can easily make a plate with a triangular cut out to vary the light falling on an LDR to measue angular or linear motion.

If you a bit handy you may be able to make and use the interference patterns between 2 fine grids (Moire patterns) - this used to be how they positioned hard drive heads (long time ago)

Grey scale, dot patterns or grey stripes allow various movements to be measured and are easy to find and print out.

Colour recognition is possible by illuminating with 3 coloured LEDS and measuring the reflectance of each to assess the over all colour.

With key in a normal keyboard give you a VAST switch array all you need to do is arrange the mechanic.

Rotary switches can be simulated with a wooden cam and a micro switch.

A wire loop with a long wire passing through makes a good touch sensor for robots. Guitar strings are a good source of fine piano wire. (dont use nylon ones!)

Card can be opunched with holes that can be read with a line of LDR/photo transistors giving all sorts of sequential combinations. Piano rolls are an example or for us oldies paper tape readers.

The possibilities are only limited by 1. your understanding of what sensors you need and how they work, 2, how cheap you are 3, your imagination.
 
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MartinM57

Moderator
curry87 said:
Regarding constructing touch sensors and the new touch functions on the new m2 picaxes is it basically 2 wires one ground one from picaxe input with a insulated plastic on top ?
Click to expand...
One wire from PICAXE 18M2 touch pin (of which there are several) to washer/piece of PCB etc with insulated plastic on top.

Need to calibrate it after installation in final position - details are in Manual 2
 
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Dippy

Moderator
I guess one thing to think about with vibration sensors is to see if you can take advantage of resonance - this can give a natural 'amplification' where practical.
And I guess the other thing is that whilst it is possible to make something very sensitive you should also ensure that overload doesn't damage it.
 
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curry87

Senior Member
@Rickharris lots of sensor ideas thanks.Will any transistor work as a light detector if i scrape off the plastic,how does that work and how do i hook it up to a picaxe input ?


Are phototransistors basically the same as a light dependent resistor just an extra pin ?


Also does anyone know a good place to find more ideas of how to build inventive diy sensors that detect vibration,movement,heat,light etc I looked on google and looked at a few books to no significant success ?
 
D

Dippy

Moderator
"Will any transistor work as a light detector if i scrape off the plastic"
- I would guess so, but when phototransistors cost pennies why waste time with a Stanley knife?? ;)

Are phototransistors basically the same as a light dependent resistor just an extra pin ?
- in reality no. They are semiconductor junction devices. LDRs don't care which way round.
Basically they are a standard bipolar transistor and you are letting light 'trigger' the base.
When used for light sensing an LDR has a far greater dynamic range. A photo-tr will saturate fairly easily (i.e. it doesn't take much).
A photo-tr has a much quicker response time than an LDR, particularly at low light levels.
You could argue that in certain circuits and certain conditions a photo-tr behaves like an LDR, but to think they are directly swappable would be a mistake.

Some photo-trs have a base lead, some don't.

If you want a fast device with a wider dynamic range look at photo-diodes.

How do you hook it up?
Do a Forum search on phototransistor - I seem to remember dozens of posted circuits.
Example: http://www.picaxeforum.co.uk/showthread.php?t=14627&highlight=phototransistor
POST #3
I'll leave you to look for any others...
It REALLY IS worth spending time searching.

Sadly, the Manuals don't appear to cover phototransistors (or transistor switched inputs) - come on Rev.Ed , this is basic stuff :)
If you look in some Phototransistor Data Sheets they should give you a clue how to use them as a switch.
Once you have absorbed that concept you'll how they can be connected in a VERY similar way as a push-button switch.

What is your level of electronics skill so that people can pitch their replies correctly ?
I would assume you are at the 'early stages' of electronics?
Can't help with books I'm afraid. But good for you for looking :)
 
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Jaguarjoe

Senior Member
To make a vibration sensor suspend a magnet vertically between two taught rubber bands. Wind a big coil of fine wire around a cylindrical tube that will surround the magnet. As the coil vibrates up and down it will produce a small voltage. You will need an op-amp to boost the signal.
 
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curry87

Senior Member
Any more ideas on a diy pressure sensor so far i got conductive foam between two copper plates and a stretched balloon skin over a container with a penny in the middle ideally one that can hide under a carpet without being noticed until steeped of course?
 
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eclectic

Moderator
curry87 said:
Any more ideas on a diy pressure sensor so far i got conductive foam between two copper plates and a stretched balloon skin over a container with a penny in the middle ideally one that can hide under a carpet without being noticed until steeped of course?
Click to expand...
Did you see post #8?
A further search on that site :
http://www.instructables.com/pages/search/search.jsp?cx=partner-pub-1783560022203827:npr2q7v5m6t&cof=FORID:11&ie=ISO-8859-1&q=Pressure+sensor

shows ten pages of pressure sensors.

Ec
 
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Rickharris

Senior Member
curry87 said:
@Rickharris lots of sensor ideas thanks.Will any transistor work as a light detector if i scrape off the plastic,how does that work and how do i hook it up to a picaxe input ?


Are phototransistors basically the same as a light dependent resistor just an extra pin ?


Also does anyone know a good place to find more ideas of how to build inventive diy sensors that detect vibration,movement,heat,light etc I looked on google and looked at a few books to no significant success ?
Click to expand...

Only the old glass capsule transistors are painted - Get a metal can small signal transistor and fil of the top.

When light falls on the base it causes the transistor to conduct so if NPN you connect the emitter to ground and the collector to Vcc with a suitable resistor in series the output if you get values right can go to a digital input. you may be able to read analogue voltages from it as well.

there is a short thread about scraping the paint off to make LDRs somewhere. I seem to think BB had a hand in it.
 
premelec

premelec

Senior Member
Rubbery Ruler

A simple but interesting mechanical capacitive sense form is found by a search for "Rubbery Ruler" ... i think perhaps the new 18M2 touch sense function could use this.. though I haven't investigated this function.

I have noticed that a good vibrational sense unit is a CD player lens aiming coils and permanent magnets... sort of a 2D voice coil unit...

Whatever works! have fun...
 
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curry87

Senior Member
How does a phototransistor compare with a LDR for detecting light level changes which one is more sensitive and precise ?

Is it possible that a light sensor could be made sensitive enough to detect the slightest of light level changes for example someone walks into a room and disturbs the light even though the human eye cant detect it sort of like a really crude motion detector ?
 
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eclectic

Moderator
curry87 said:
How does a phototransistor compare with a LDR for detecting light level changes which one is more sensitive and precise ?

Is it possible that a light sensor could be made sensitive enough to detect the slightest of light level changes for example someone walks into a room and disturbs the light even though the human eye cant detect it sort of like a really crude motion detector ?
Click to expand...
My last post on this thread:

Why not just spend a couple of quid
and do a few breadboard tests?

You'll learn so much.

And, I say this genuinely.

e
 
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TCLynx

Member
I might be jumping in where I have no business but if you are looking for possible household items that could be turned into sensors.....

If you have any old microphones or headphones lying about, then you already have a magnet and coil attached to a thin surface that could pick up sound and/or vibration.

Now myself personally, I would probably go to radio shack and get a pair of the infrared emitters/receivers (I know I probably called them the wrong things but I expect everyone knows what I mean) but if you are forced to only use things you might find at the house, well if ya got an old VCR with a remote that doesn't get used anymore, perhaps you could steel parts and set up a infrared beam that when broken would cause an alert. Heck, I don't know maybe some of those parts wouldn't even need a "beam" in order to notice something moving.
 
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Rickharris

Senior Member
curry87 said:
How many kinds of sensors could be constructed fairly easily with the bare minimal components needed and still be fairly accurate without buying a self contained module off the self that does it for you ?
...
Click to expand...
Someone should ask you - WHY? The components are not that expensive.
 
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Dippy

Moderator
Curry: "Is it possible that a light sensor could be made sensitive enough to detect the slightest of light level changes for example someone walks into a room and disturbs the light even though the human eye cant detect it sort of like a really crude motion detector ?"

As said, try it. It's the only way you'll get an acceptable answer.
There are just so many variables that no-one can give you a definitive answer and as your technical knowledge is at the early-stages level you will need a lot of help.

Many things are possible but the number of flase-triggers should be amusing.

Sounds like you are floundering around trying to invent an intruder alarm or people counter on the cheap.:rolleyes:
If I were you I'd sit down and think of possible methods and then look at the Real World pros and cons of each method.
Or you could just keep posting ideas here and let others spend hours assessing them...
 
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Andrew Cowan

Senior Member
curry87 said:
Is it possible that a light sensor could be made sensitive enough to detect the slightest of light level changes for example someone walks into a room and disturbs the light even though the human eye cant detect it sort of like a really crude motion detector ?
Click to expand...
Not really. It would also detect clouds moving across the sky, someone walking past the window, shadows from planes, birds etc. It might work in a room with no windows (a basement?), but even then I'd expect it to give plenty of false alarms.

A
 
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gengis

New Member
Simplest vibration sensor: glue a weight to a speaker - great for low frequency like autos, footfalls, and seismic activity. Mount it with the weight down in a grounded metal can and bury it a foot or two deep. Takes some amplification to get useful trigger outputs, but can output a volt or two if the vibration is sufficient.

It is easy to sense people or moving objects with visible light. A tapped photocell and lens is all - into a bridge circuit with an opamp. It can ignore light level changes that affect both sides of the bridge - like lightening, or ambient light. The principle and circuitry is the same as used for passive IR detectors. (the signal v is either up or down depending on which side is seeing more light and the trigger has to respond to either polarity - just like a PIR sensor) Downside is that it responds to any movement not just warm blooded animals.
 
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