The weather for today

Today I finished the PSU for the peltier element and connected the stm32f103 to the thermistor (the stm32f103 is still not measuring the voltage over the TEC). And here are the readings (sorry for the blurry photographs):

First, before the TEC was turned on:

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It’s fairly hot in DK at the moment. The ambient temperature is 25-26°C.

Then after 5min with the TEC on. The voltage drop over the TEC is app. 8V, I have no idea what current draws, but the transformator is rated at 4A:

DSC02531

So it reaches a temperature difference of around 10°C. Not as much as I had hoped.. With some heatsink paste between the peltier element and the aluminium plates the temperature dropped another 1.5°C, still not anywhere the expected ΔT of 30°C.

So good animals are uncooked, as we say here in Denmark. I had a second look at the audine project to see if I had missed something. Most likely I have, but I didn’t find anything suspicious about my setup except that the TEC 12706 protrudes slightly on the cold side. I had some smaller TEC’s from another shopping spree, most notably the TEC 03506. You see the difference in size here:

DSC02541.JPG

And with the little one, it’s an entirely different story. The voltage drop across the smaller TEC was around 5.6V and the temperature difference was much greater. The CCD started to collect condensation, which is around the time I stopped the test:

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The temperature at this point was -0.6°C 🙂

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8 thoughts on “The weather for today

  1. david_uwi says:

    Do you have any idea how flexible the timing is on the arrays?
    I have been fiddling around with ADCs that I have to hand and most will be too slow (12 us conversion for 12-bits is the fastest).
    I’ve also got one that is stupidly fast (but only 8-bit) which will cause problems in capturing the data.
    I’m attempting to use a TCD1103. I have previously used a TSL1402 which despite the stated clock rate will follow the imputted clock pulses no matter how slow allowing me could use the timing and the internal ADC on a PIC16F1788

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  2. david_uwi says:

    Sorry if my question was a bit confusing.
    I have got round to connecting up a TCD1103 diode array. I am getting two problems first the logic voltages from my microprocesor are being dragged down to unacceptible levels. Second I am looking at the data sheet and it has logic inverters on the pins – is the logic inverted?

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    • It sounds like you got it working without my help, but I’ll answer your question regardless 🙂

      The timing diagrams in toshibas CCD datasheets are not inverted, they show the signals as the CCD should receive them. It’s however correct that they suggest (at least the ones I’ve seen) that one uses a logic inverter between the MCU/clock-circuitry and the CCD. This way you can easily convert 3.3V to 4.0V (the case for the TCD1304), but you will of course have to invert the signals, so that they are inverted back to normal before reaching the CCD.

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  3. david_uwi says:

    Finally got it to work (there was a short on the PCB – my soldering).
    Though the datasheet says the minimum clock rate is 400 kHz it still works at 100 kHz (but with a long integration time). So a fairly pedestrian ADC can be used after all.

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  4. david_uwi says:

    Yes there seems to be no limit to how slow you can clock. The device just waits for the clock signals.

    I’m a bit worried that by underclocking I ill have a much too long integration time. So I am going to look into using ths shutter.
    Is there any advantage in using a transistor on the output (as suggested in the datasheet) I would think it just introduces non-linearity (which I do not want as I am trying to make a visible spectrophotometer).

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    • I’m not an electrical engineer so I can’t answer this question. I assumed it was there for a reason (low impedance output?). I’ve successfully substituted it for an inverting opamp (https://tcd1304.wordpress.com/adc-input-conditioning/) to match the range of the output to the input range of the ADC, and someone somewhere (hackaday I think) said the opamp would have a zero (or close to zero) temperature coefficient. You can also take a look at the work of david allmon.

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