Alex Tsekenis

I hate this about academic environments. Anyway, you could claim that a preliminary goo must be produced to verify the feasibility of a method to measure the conductivity of the goo.

Do you need a digital or analogue display paulhyi? What range of currents?

Apart from agreeing with Hero's post have a look at these links: http://www.elecfree.com/Battery%20Monitor%20for%2012V.php http://www.electronics-lab.com/projects/automotive/009/index.html http://www.mhennessy3.f9.co.uk/battmon/index.htm You can also modify your circuit to use a duo-colour LED. Green when the battery is high, orange when half full and red when empty. Also, there is the Bible of batteries that you can reference for an open terminal voltage VS remaining charge for lead-acid batteries: http://www.amazon.co.uk/Handbook-Batteries-David-Linden/dp/0071359788/ref=sr_1_1?ie=UTF8&s=books&qid=1261596112&sr=8-1

So similar... Thanks audioguru for pointing this out.

I used to build such kits since I was 10 back home in Greece. My first kit was this: http://www.smartkit.gr/details2.php?lang=1&wh=1&the1id=1&the2id=6&the3id=29&theid=29&open1=1&open2=6&open3=&thepid=122 A 555 based led flasher, which didn't work due to cold solder joints (my first solder iron was a 120W pipework tool from my grandpa). Anyways, I have built the 4-Watt kit pictured and I can still recall the schematic more or less. Such kits from SmartKit are imported in the UK by Quasar Electronics. I have seen other copies of SmartKit kits in the projects section of this site so I am not surprised. The kit pictured had a microphone input and an amplifier around it (the T0-92 transistor). I really can't recall if any emphasis circuit was employed, I would have not recognised it back then anyway. I can check if you really need to know. I do remember that it was a pain to tune the circuit using those variable capacitors and that a stabilised 12V source was needed. I used this kit back then: http://www.smartkit.gr/details2.php?lang=1&wh=1&the1id=1&the2id=6&the3id=32&theid=32&open1=1&open2=6&open3=&thepid=144

That circuit is part of this kit: http://www.smartkit.gr/details2.php?lang=2&wh=1&the1id=1&the2id=6&the3id=39&theid=39&open1=1&open2=6&open3=&thepid=206 and the text was originally in Greek. Anyway, you can have a look at the coils on that PCB, there is one on top marked RFC2 but the circuit doesn't care what the component looks like so you can use something else with a small inductance value as Hero pointed out. In the original instructions you are required to wind a coil using thin wire around a 1MOhm resistor. Obviously inductance is not too critical.

OK, here is a picture of the lot. Check your PMs for more info.

I have come across some integrated colour detectors, 3 photodiodes with a colour filter. I have never used them so I can't comment further. Here are some: http://au.farnell.com/jsp/search/browse.jsp?N=500001+1002850&Ntk=gensearch_001&Ntt=colour&Ntx=mode+matchallpartial They are very expensive so maybe you could copy the technology using discreet photodiodes and colour filters. You will need to calibrate the set-up as the sensitivity to each colour will be different. Sorry for using the Aussie site, UK one was unavailable.

Your schematic looks OK. I think you can get away with increasing the value of R3 to a few kOhm unless your relay's coil draws something like 6W. What did you have in mind with D9? Is that there for protection? Finally, the zener diode at the gate of the IGBT. Maybe you dont need that if IC2 has internal clamping diodes to +12V.

You do not have current in your circuit as current flow would be a number of charged particles (electrons here) passing through a section of your material and having a common net direction. As I understand it, your electrons are bound in the material but not to a specific atom, much like a conductor. My best bet with my very limited knowledge in this field would be to measure the conductivity or a similar quantity of your material. The more 'free' electrons, the higher the conductivity. The circuit you linked is kind of the electronic equivalent of your polymer. Unless you tell me that this is the only solution I cant see how you can use this circuit with its current component values. How about sending me some of your photoelectric goo :P and I run some tests at uni or home? Maybe putting it on a glass substrate with two electrodes on each end.

Hi Stuart and welcome to the forum. Thank you for your input. Your contact seems to be multidisciplinary so the book should be a good overview/introduction of/to electronics.

And just to expand on Hero's post below, this is the topology of the ICs suggested earlier in this topic. You can google hysteretic LED driver for more info, Elektor Electronics (the magazine) published an article this year too. By adding a resistor in the LED's path you can sense it's current and modily your duty cycle.

You dont need to know so much for a functional SSTC, but I like your mindset. In fact, if more people with your mindset entered higher eductation I believe the world would be a different place. This book: http://www.amazon.co.uk/gp/product/0471226939/ref=sib_rdr_dp is highly regarded in academia as it contains ample theory on topologies and semiconductor devices. But my god that is expensive. Maybe you should review it in a bookshop before buying it. This book: http://www.amazon.co.uk/Switching-Power-Supply-Design-3rd/dp/0071482725/ref=sr_1_2?ie=UTF8&s=books&qid=1261473687&sr=1-2 Is a good blend of theory and practical application hints for SMPS. However it doesn't go into as much depth in transformer design as this book: http://www.amazon.co.uk/Switchmode-Handbook-McGraw-Hill-Eletronics-Handbooks/dp/0070067198/ref=sr_1_1?ie=UTF8&s=books&qid=1261473687&sr=1-1 Maybe a book on SSTCs will bring all this knowledge together. For EMI, this is one of the best, good layout: http://www.amazon.co.uk/gp/product/0824789245/ref=sib_rdr_dp But this is cheaper and maybe you dont need all of the knowledge in the book above. http://www.amazon.co.uk/gp/product/0750672331/ref=sib_rdr_dp For general electronics I dont think there is a single book that even scratches the surface of the science. There are some good books that focus on circuit analysis and a few others on analogue electronics. I have found myself learning basic principles from different sources and then I find specific books relevant to each project. Maybe the Art of Electronics is worth reviewing.

No, no reason why you couldn't do that. But do you want to do that? Once the transistor is ON, your output will shoot to 12 V (assume car battery) and there is nothing you can do about it by changing the duty cycle. When the transistor is OFF your output volatge will fall depending on component values. You can't regulate this system. Anyway, constant voltage drive is not suitable for power LEDs. You need constant current drive (see suggestions below). Attached is a waveform of the output voltage of your proposed system to illustrate my point. Also, see what I came across: http://www.amazon.co.uk/gp/product/0750683414/ref=sib_rdr_dp Prob. an overkill.

Yes, a 1MOhm resistor. Maybe you will have to tweak the value a bit. Ok, so no rule of thumb, read datasheet if available or test each LED experimentally.

Ah yeah, I remember, dodgy LEDs. Probably that's it then. Since your photodiode is transparent(?) the lead that does not contain the actual semiconductor should be the anode. I have found this to apply to dodgy LEDs even if they have non-standard leads. Let me know if you have found any LED or similar diode that doesn't follow this rule so that I don't assume it anymore. http://upload.wikimedia.org/wikipedia/commons/f/f9/LED%2C_5mm%2C_green_%28en%29.svg

Very surprised this did not blow up. The photodiode is forward biased with 5V - 0.8V across it. A massive current will flow in the base of the transistor. If it doesn't blow up it doesn't mean that it works or that it is a good design. So, you either try Hero's suggestions below and attempt to add hysteresis or try a comparator circuit with hysteresis which also means that you can throw away all NOT gates.

Maybe a comparator circuit with a bit of hysteresis using a CdS cell or a photodiode? http://home.cogeco.ca/~rpaisley4/Comparators.html

Or he fixed his lights and didnt say thank you.

Well I am sorry, but there will always be a degree of inaccuracy and your synthesis method will not be any better either. You can use statistical methods to further increase accuracy/precision. At your desired resolution and signal levels noise will be dominant which translates to highly engineered instruments i.e. expensive and potentially bulkier. The equation below can be as accurate as you want it to be, if you have accurate input you will get accurate output. Maybe you can overdope the polymer with crystals to get a measurable output and then extrapolate based on some model from your theoryto estimate the effects of lower concentrations?

I see. No that camera looks ideal since your board has a composite video signal input. I see from the schematics that, following the standard, a transceiver is used for the RS232 link, so you immediately need a similar IC on the side of your PIC, possibly the same (get samples from Maxim for free) I can't comment on what would be a good resolution for your application. However, your blimp will be quite high and your camera optics are quite poor, so maybe a higher resolution is desirable to perform digital zoom? Also, I wouldn't say that the application is not required to respond in 1 second if there is a fire, I mean fast response is not a priority, valid identification of a fire is more important though.

I think I have seen that curve tracer in some dark and humid lab in the university of Manchester. Maybe I could look for it, they can use the newer ones I guess. ;) How badly is this wanted?

That is painful. Maybe you could do this more indirectly. For example, you could look for an instrument that measures conductance G and since your material geometry will be known you could use this: σ = (G * length) / A [sm-1] For example the Fluke 289 can measure down to 1nS (1G Ohm). Try plugging in your geometry and see what sort of conductance range you might require from an instrument.

Sure, you could pass digital signals down these lines. However you might have an issue with any DC-blocking capacitors in the audio signal paths on the DSK board. The other way would be to use an ADC/DAC and go analogue. I am sure there are other ingenious ways to use these ports for data, but why cant you use the expansion ports on the board itself?

You could use a normal constant current source which will be quite inefficient, you could use a hysteretic driver much more efficient or you could use very specialised ICs based on hysteresis again like the new LT3743 or the MAX16818. These are in order of increased complexity. But I am sure there must be a ready product that meets these specs. That is where I would start.