Thoughts on networking the smaller PICAXES

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ciseco

Senior Member
Dr A,

You and I think alike so much, I'm planning to do a 12v ring around the house :)

I already have my office and 1 room like this. I use DC-DC converters instead of wall warts for wireless kit, router etc. My 2003 server (consumes 11 watts) runs at the native 24v+ of my battery bank (I have a Lister CS, 1/2Kw solar panels and a 1Kw wind turbine) planning to build a babington and a steam engine (yep sounds crazy but the mathmatics work perfectly, the lister is actually too efficient, I need more heat than power as I only use about 6Kwh/day or a steady 250w averaged out). Waste veg oil is getting difficult to find, waste motor oil in a bab might be a better option.

I've love to see if it's possible with peltiers to generate the 250w, anyone know much about them?

I'll be writing up the documentation on the electricity monitor in the next week if anyone else fancies building one (less than ?2 in componants)

Cheers

Miles
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Honda NX650
 
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moxhamj

New Member
Cool Miles. If you are into solar and alternative power, a 12V supply in each room makes a lot of sense. Lots of things run on 12V as this caters for the whole RV/camping industry. I wonder what sort of socket you would use - something that looks ok ie similar to a mains socket?

Re data comms - I'm running wires but I'd like to get wireless reliable enough, as wireless has a lot more flexibility.

Peltiers - going off topic I know, but they are getting cheaper and cheaper. I did a cost analysis last year and I think they were similar to solar cells. So they cost more than solar if you then add the cost of a solar concentrator. But, on the other hand, if you have waste heat already then they could be quite attractive. I'd grab one and do some tests. Biggest issue is cooling. Either some big heatsinks with fans (careful the fan doesn't draw more power than the device produces!), or a big lump of metal and then water cooling. I think there are demo projects around where they were used on the exhaust of trucks.
 
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ciseco

Senior Member
Everything at the moment is wired ad hoc, hence why only two rooms, the misses hates wires :)

Water cooling peltiers would be perfect if they are fine to 50C (the hot water tank temp) then essentially you could air heat with a stove, cool with the tank water (as a bonus) and get electricity (as a bonus).

I've a really old house so heating is the major cost.

Are they any where near as efficient as solar? ie would I need 3-4 sq mtrs of them to generate 250w, thats a BIG stove, could burn tree stumps in that :)

Miles
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AutoAlliance International
 
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boriz

Senior Member
I had an idea. How does this sound…

When the ATTN line goes high, all the AXEs jump to their ‘you talking to me?’ routines. In this routine they monitor the data line using PULSIN. Each AXE has a unique address and that can be translated to a unique PULSIN duration. The TX AXE raises the ATTN line, pauses a few ms to make sure everyone is listening, then does a PULSOUT with the duration set to the ID of the target AXE. All the AXEs on the network receive this pulse, but only one of them will recognise it as the correct length to indicate itself.

Pulse durations will be scaled by a factor (f) for reliability. Say f=2. So for AXE1, it’s ID is 1, so it is looking for a pulse duration of 1*f, a duration of 2, or 20uS. AXE2 is looking for 4 (40uS), AXE3 for 6 (60uS) etc.

All the other AXEs return immediately to their main processing loops, but the AXE identified by the pulse goes to it comms Routine. Now two AXEs can chat away, all the time keeping ATTN high.

To prevent other AXEs from repeatedly returning to their ‘you talking to me?’ routines, an ‘ignore ATTN’ flag will be used that gets reset when ATTN returns to low.

Any good?
 
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Dippy

Moderator
For something like this I would do the 'you talking to me?' part as you as say, .. brief pause so all slaves have time to pop into Serin. Then Master Serouts with dummy byte, then the address/request and a spare byte to clear any blocks in slaves. Only the target PICAXE replies, the others say to themselves "oh, not me then" and carry on.

Actually I've done very similar with a few PICs in a pier2pier arrangement and it works fine. The only difference was that i used the buffered serial in and each PIC interrupted and popped into the Serial-Read routine. Very similar except you use a secondary wire.

Try it.
 
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manuka

Senior Member
Although semiconductor based Peltier effect devices are ideal for precision heating/cooling, their conversion efficiency is quite PATHETIC- a few % would be typical. Thermoelectric effects are 2 way of course, & historic thermocouple/pile sensors indeed give a few mV output with temp diffs of 10's of degrees. However attempts to generate useful electricity by exploiting just modest temp. differences are akin to harnessing moonbeams !

However- I recall reading of a WW2 era Russian battery charger that clamped around a stove chimney (with maybe the cold junction in the snow?), but armfuls of wood & a blazing fire were needed to get things ticking along. A 1980s Scottish approach with camping gas springs to mind now too.

EXTRA: If you have a big old house the obvious thing to do is INSULATE IT, & thus reduce your space heating energy needs. Dippy - P2P means peer not pier- you maybe have Southend on the brain still?
 
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Dippy

Moderator
Oh Stan, 4give me. I won't back and edit it but you're completely right. How embracing.

Actually, quite a coincidence...
I went to Southend the other day and walked under the pier.
This scantily clad woman walked up to me and said "Hello darling, do you fancy a bit for 20 quid?"
I said "I didn't know they were knocking it down."

I, too, can't understand the reason for trying Peltier for power production. It's an interesting exercise. I'm sure there are circumstances, but strapped to a house isn't one of them.

EXTRA: A friend and missus bought a new house last year. Covered in insulation and hermetically sealed everything. Bl***y awful. No ventilation so you can smell last weeks curry.

EXTRA2: Boriz, why not try something and get it running b4 you get thousands more suggestions. Different people have different preferences and different ways of explaining things. If I were you I'd switch off the Forum and have a go. It shouldn't explode.
 
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slimplynth

slimplynth

Senior Member
air is a very good insulator if you can stop it moving about.

Went on a plastering course a couple of years ago so I could modernise my own house... old house with high ceilings = cold winters. lower the ceiling using plasterboards etc... materials cost about 150 quid. easily added some cool looking halogen down lights, one in each corner and one in the centre.. hold on thats 250W... not very energy efficient.. but it does look nice :D
 
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Dippy

Moderator
And, of course, you can also run your network cables in the cavity...

I'm sure you could have got cheaper plasterboard from Ebay.
 
slimplynth

slimplynth

Senior Member
I'm an impatient devil though.. quicker to goto the local builders merchants. Good quality boards, dabbing compound and two bags of multi-finish plus a credit card and a bucket of sweat an tears were all that was needed ;)

Unfortunately, I did it pre-picaxe so only had the foresight to lay speaker cable for recessed ceiling speakers in every room, these will be eventually be PIR triggered so that the melody follows me around the house. The impatience cost me though as I'm now struggling with 433Mhz, getting stable signals to an from upstairs - Karma loves me:p.
 
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Dippy

Moderator
With a bit of skill you could m-plex serial down your speaker cable.

Struggling with radio through plasterboard? Is it that foil backed stuff or something?
 
slimplynth

slimplynth

Senior Member
In no way asking for help but if its obvious...

Cheers dippy but I'm starting to think its something I've done wrong, physically, with either the transmitter or reciever circuit. The ADC values I'm sending (even 1m away) are debugging erratically on the reciever side but when I connect the transmitter with the AXE027 its debugging steady values.

Have got a few things to try before I have to be brave and start a new thread asking for help, **thanks everyone in advance :D** might just order a new pair from sparkfun to start with, I'm using these... 2400bps - 434MHz but has anyone used the 315Mhz tx/rx pair? I'm guessing they are less prone to interference having a larger wavelength.

After typing all this I'm starting to think I should have just started a new thread and posted code, diagrams and detailed report.. but like i said in the title I'm not asking for help... The struggle is half the fun, the other half being a warm glowy feeling when it all comes up Millhouse.
 
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moxhamj

New Member
433 vs 315 isn't much difference. The problem is more likely to be one of two things - 1) the antenna is not the right length (how many cm are you using), or
2) the modules are a bit enthusiastic with their range claims.

I've learnt to translate these modules claims - 50m = 10m, 1000m = 200m and 4000m = 500m. Seems to be fairly consistent between lots of different brands. I suspect they are all quoting ranges based on a transmitter transmitting to a very sensitive scanner and listening for a tone using an ear. Sending data is different.

So just up the power a bit. http://www.instructables.com/id/Build-a-500-metre-radio-data-link-for-under-40./ and look at the module on step 7. This is rated for 1000m and so in the real world it goes about 200m and should be able to get through walls etc. (Don't use the 4000m one - it is overpowered for inside a house and you need to move the antenna away from any electronics). Also, that receiver on the instructable is the best one from that company by a big margin. I chose that supplier in China because they happen to have the cheapest price per reliable metre of data communications.

Plus, you need some test code so you can set up a transmitter, transmitting a packet every 5 secs or so, then a receiver with a battery that gets the packet and does a checksum and then flashes a led. Then you can wander round the house and test you can receiver everywhere.
 
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ciseco

Senior Member
Navitron sell a camping light with a radio just like that russian thing, surprising what goes full circle :)
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RC113
 
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moxhamj

New Member
Just to clarify what I think was said before, peltiers are not great for producing power. When the watts are quoted - eg a 50W peltier, this is its heating or cooling power. When you use it in reverse, thermodynamics says you can never get more than Carnot efficiency, and peltiers are a lot less than Carnot. You might get 2-3%.

Thermodynamics is really really complex, but to simplify, with small heat differentials you can use a small amount of energy to pump a lot of heat (eg a reverse cycle air con), or you can use a lot of heat to create a small amount of energy. With big heat differentials (hundreds of degrees K), you start to get more energy out of your heat engine. But then your engine needs to run hot, and that becomes a materials problem.

Peltiers run at "hot" temperatures, and while you do get electricity, they are not as efficient as, say, a stirling engine or a steam engine. But they are simpler.

Say you have a 1000W peltier, and you are getting 2% energy out, eg 20W. You still need to move 1000W through that device. The problem becomes cooling the cool side, because you need to dissipate 1000W of heat somehow, with a small temp rise. You can use big heatsinks (expensive), or you can use fans (there goes the 20W you just created), or you can use cooling water. What you need is a cheap and limitless source of cool liquid, and it is no accident that power stations are usually located next to rivers or the sea.

I think water cooled peltier generation could work, but I'm not so sure about air cooled. The cost of metal needed for the heatsink area becomes prohibitive.

Of course, if you only need 0.1W to drive a bright led, then it could be done. Solar is cheaper though.

Re Spike Milligan and the Goons: Neddie Seagoon - "What what what what what what what what what what?"
(To which Grytpype-Thynne usually replies, "Only ten watts? You're not very bright are you, Neddie!")
 
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ciseco

Senior Member
Dr A,

I understand, I'll give you what came to me, lets start with a nominal 9Kw (my stove at full) of heat, at 4.6% efficiency for the peltiers. We could expect through 17 devices just over 5Kw needing to be transfered through the pelt and into the hot water cylinder (the very useful by product of cooling the backside of the device). This would allow me to "steal" at this point something around 234 watts, which is almost the 250watts per hour my house consumes if you average out the 6Kwh I get through daily.

If the stove was on for 4 hours in the evening, I'd get some local heat, some electricity and some hot water, all in actually useful amounts and from many different fuels.

I've got a Lister CS for CHP and although it's design dates back to 1929, it's like any other ICE too efficient at turning fuel into motion, like others I'd have to load it with 3Kwh of electric bar heater to give it something to get it's teeth into whilst recovering about 30% of the residual heat gaining an overall efficiency of about 60%, but when the fuel is free, this is less of an issue but coming by free waste oil is getting difficult.

If we take my house for example, I need an average of 49Kwh of gas yet only 6Kwh of electricity, if I could "release" 12% in the process at source I could generate all my own electricity.

I am familar with sterlings, and yes, possibly a much better bet aka wispergen, but you certainly can't buy a sterling off the shelf (for that possibly any other than the models) that would achieve 250w (estimated before at 1/2 size of the fabled ST5), cost a potential ?221 GBP and take as little space as the peltier. I've seen prices of ?18K for them, thats a huge pile of nearly 1400 TEG's in comparison and you cant put cheap logs into a WG :) natural gas only :(

A steam engine in my mind is the most likely candidate for the hobbyist with heat recovery for hot water, it would still be very difficult to find something reasonably priced too, then add safety into the equation, the TEG's actually represent a real alternative with all these factors taken in.

Then again I could be wildly wrong, as proved in an earlier post my mathmatics isn't always what it could be :D

Miles
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Chrysler picture
 
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Dippy

Moderator
Just use a solar PV panel to power a Peltier to use as a heat pump for solar heating.
Only kidding.
I never got round to doing my solar powered steam engine. That would have been a nice project.
 
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ciseco

Senior Member
would that work?? ;)

hehehehe, I've seen similar questions before, it's usually akin to, can I wire up a ?10 maplin solar cell to my oil filled radiator?

As last nights silly postings, reminded me, we all start somewhere and there's always someone who much much knows more. The only thing anyone of us can claim infinate knowledge of is our own thoughts :)

Are you into renewable energy then?

Miles
________
marijuana vaporizer
 
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Dippy

Moderator
Dunno.
If you think about basic Thermodynamics heat flow is greatest when there is larger temperature difference.
A compressor (fridge style) heat exchanger is very good as the heat exchange includes a contribution from the phase change. A level physics.
A Peltier gives a similar heat-exchange effect though not as efficient. But it has no moving parts etc.

Your average 'cheap' solar panel runs water through the solar panel, where it gets warmed up , and then is pumped to a storage tank where it warms up the water in the tank.
Obv the warmer the water in the tank then, for a given temp of water from the panel, the heat transfer is less.
Also obv its a bit more complicated than that as, in reality, the total system heat and temp will increase (on a sunny day).
So, the hotter the pumped water then the greater the heat transfer into the storage tank.
If the sun isn't very strong then there won't be any benefit.
Hence a compressor/peltier heat exchanger.
Also it means that the water entering the solar panel is cooler and therefore it will 'absorb' more heat in the panel.
A heat exchanger requires power. So, what's a good power source?

A contra argument would be that the heat exchanger provides the most benefit when the sun/daylight is lower, so maybe a PV Panel with auto switch to mains.
But for saleable-to-public the regs for mains powered devices are strict, I was merely suggesting an all Low Voltage idea.

I'm sure its already being done as it is so obvious to any schoolboy, I haven't looked.

It could be another product eh?

PS. Stirlings are wimps ;) I was thinking a mini power station type arrangement with a micro-boiler.
 
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moxhamj

New Member
Re "I understand, I'll give you what came to me, lets start with a nominal 9Kw (my stove at full) of heat, at 4.6% efficiency for the peltiers. We could expect through 17 devices just over 5Kw needing to be transfered through the pelt and into the hot water cylinder (the very useful by product of cooling the backside of the device). This would allow me to "steal" at this point something around 234 watts, which is almost the 250watts per hour my house consumes if you average out the 6Kwh I get through daily."

And "Free fuel"??!

How does that work?

Ok, say you can get free fuel. It does exist. My sister married an army chap, and he got an Australian attachment to an English army unit posted in Germany, and they got free fuel on the base. I wish I could get free fuel though...

Anyway, say you do have free fuel. You can't really use the cooling water to make hot water. Well, you can, but once the cooling water gets hot, you don't have as much of a heat differential and then the peltiers don't produce as much energy. You need to grab your cool water, run it past the peltiers and discharge it slightly warmed. 10C or 20C warmer max.

But if you have cool water, and you have a big supply of it, pumping cool water uses little energy compared with its cooling effect.

The great thing about peltiers is you can test this on a small demo scale. Get just one device. Build some sort of cooling loop. Strap it to a hot source and do some tests.

Re a cooling loop, I had a bit of a crazy idea of getting a metal cake tin, putting some copper pipe in it in a few coils, then filling it up with molten lead. Hopefully the lead would bond to the copper (solder does, for instance, if the copper is clean and oil free). Then you have a nice big flat metal surface that you can keep cool with water.

Right now, if you have a Lister, you have a source of lots of heat, but no cooling sink.

I'm blessed with the opposite. I have no Lister, but I do have a dam with 1 megalitre of water that is never higher than 18C.

For a heat engine to work, you need both a source of heat, and a cool sink.

Mind you, if I had a Lister that needed a 3kW load just to keep it happy, I'd be getting a big battery bank, run the Lister at full load to charge the batteries, then switch it off. Way more efficient than extracting energy at peltier efficiencies.

Oh, and re networking picaxes, I've got some boards that are in transit at the moment that I'll hopefully be soldering up in the next few weeks and testing some network ideas. It is very close to working now (all but the analog outputs are stable), but I want it perfect before publishing.
 
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boriz

Senior Member
On water heating/cooling.

I saw a fabulous device demonstrated on a TV program called Science Shack. The presenter, Adam Heart-Davis, had a hot bath in water taken from a nearby stream.

The heating method, that is also a cooling method, involved spinning the water (from the stream) in a no-moving-parts sort of centrifuge thingy. They made it out of a cylindrical block of metal with a hole through the axis (like a pipe with thick walls) and holes drilled from the outside radius to the centre at an angle to the radius, so the water fed into these holes would enter the center at an angle causing a tornado like vortex of spinning water in the centre of the ‘pipe’.

The cooler water is heavier and ends up on the outside of the vortex, the warmer water on the inside. A carefully placed ‘tap’ draws water out just in the very centre of the vortex. This water is slightly warmer than the water entering the device. And the left over water is slightly cooler.

Of course, the water has to pass through this device several times to make it hot enough for a bath, but it works!. The heat actually comes from the stream. All that is needed is a pump. They worked out that the power used by the pump is less than the power required to heat the water by more direct means. Efficiency would be improved with proper insulation etc.

Neat eh?
 
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eclectic

Moderator
Cheers Boriz.
I watched the first two of those video clips.

I nearly fell off my chair laughing!

But, if I pay lots for one of these devices, could it lift me back
and give me free energy?

Thinking ahead. Hmm? A free-beer machine?

e.


You Can't Get Ahead.
You Can't Break Even.
You Can't Change The System
 
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ciseco

Senior Member
Tesla turbine anyone? got a pile of old knackered 9.1Gb scsi's going spare and many finger removing neos out of them :)

Perhaps for one of those new fangled magnetic motors that do over unity :rolleyes:

Glad the humour has returned, yesterday wasn't fun.

Myc sorry about all that, I got deffensive far too quickly, it's just I'm passionate about what I'm doing and hand on heart am not out to fleece anyone, so I felt I needed to justify myself. I should let time be the judge and jury on that one and pipe down more often, again appologies.

Finished the meter pulse reader, needed a little amp to chase those quick flashes, here it is if you'd like to build one.

mmmm, i cant seem to place images inline from phpbb, here's alink that might work.





whoops spotted a mistake, pot should have been to the wiper not the end, will change it in the morning




Miles
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Subaru Exiga specifications
 
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boriz

Senior Member
Converting heat into electricity is a great idea. Especially if you subscribe to every catalogue and junk mail producer you can find. Free fuel delivered every day to your doorstep. (Neat idea. Not mine tho.)
 
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ciseco

Senior Member
hehehehe, I so like that idea boriz, less fanny by candle light, more toastie by ikea, argos, yellow pages, next and everyone else that publishes reams of stuff I'll never buy.

Once did try burning an awful lot of paperwork, just wouldn't go, so I whirled a large dose of fresh air into a bottom hole of the incinerator via a compressor, never knew you could paper burning that hot, the metal was well above orange and in the centre it was somewhere high yellow.

Miles
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extreme q
 
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Rickharris

Senior Member
Dippy said:
Just use a solar PV panel to power a Peltier to use as a heat pump for solar heating.
Only kidding.
I never got round to doing my solar powered steam engine. That would have been a nice project.
Click to expand...

Yep it works (with enough sun - An iron tube of suitable dimensions (not mentioning in case anyone tried to do this and I get sued) Big lens to focus sun (big yell thingy we are not too familiar with in the UK) onto the tube.

Feed water in the bottom at a suitable rate - Flashes to steam which exits at the top. Drive steam engine - video here http://www.youtube.com/watch?v=uJGpbvvJA2I

Can't see a 4-6-4 ploughing up the main line on sun power though.
 
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ciseco

Senior Member
thats a ruddy great fresnal, with one not much bigger than A4 I can vaporise concrete in full sun here in tropical (not so) nottingham

A two axis tracker would be fun to get right and still keep it that focused, bit more precision needed than a panel tracker :)

Any one wishing to play, word of warning about retina damage from looking at what you are trying to burn, and I'm being serious, look into a luxon high power LED thats just a few watts and then watch the dots in your eyes, with something that big you might be releasing 100's of watts on a pin head, please be careful

Miles
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buy silversurfer vaporizer
 
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boriz

Senior Member
Another idea. No checksum required. You send every byte twice then XOR them. If you get a non zero result, corruption has occurred. That should be pretty bombproof.
 
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