First steps towards a new PCB

This entire time I’ve been content with the very simple drive circuit from the TCD1304’s datasheet:

tcd1304 typical drive circuitIt has a low parts count, it’s easy to understand and it performs reasonably well.

However, after reading through the Audine project, I’ve realized how elegant TEC can be done, and how inelegant I had planned to do it. So I decided to make a new PCB with a cut-out for a cold tip, and while I was at it I also wanted to try David Allmon’s solution for conditioning the output to the ADC.

And here it is:

Of course it doesn’t work.

Or rather, the MAX232 is not able to supply enough current for the AD8021 op-amp. This really shouldn’t have been a surprise, but I hadn’t been paying attention, neither to the datasheets nor to the changes in Dave Allmons new circuit.

So off with the MAX232 and in with an improvised ±9V supply for the op-amp:

And then it was time to try and collect an exposure:

It may not be clear, that the reading is no longer upside-down, but if you don’t want to take my word for it, look at the dummy-pixels at either end of the CCD. They used to have around 3900 in value, now it’s closer to zero.

It’s not evident from this capture, but the values of saturated pixels are now around 3000. The ADC is 12-bit and has a range of 0-3.3V, so there’s a few bits of resolution going to waste. It can be fixed by turning up the gain of the AD8021.

Oh, and there’s the cold tip to introduce as well:

It’s just a piece of aluminium that used to be 20x30x50mm before I started sawing into it. It looks better from this angle:

Up for next time is the new and improved PCB with separate analog and digital power, but it will take a couple of weeks for the boards to arrive..

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