Pico Puffer

RE: Pico Puffer

dougw — Mon, 16 Aug 2021 19:26:46 GMT

Your project is looking good.

If you use 2 metallic probes, each in a separate plastic bag, you can put water in each bag to eliminate air.

Actually only 1 probe needs to be insulated with a plastic bag, the other probe can contact ground moisture directly.

RE: Pico Puffer

robogary — Mon, 16 Aug 2021 16:48:00 GMT

Cool project.

Its great that Pico Puffer got to enjoy some beach time this summer. I'm jealous :-)

RE: Pico Puffer

michaelkellett — Tue, 10 Aug 2021 08:51:33 GMT

I did a similar thing a while ago, I wanted to measure crosstalk between electrodes in an electrostatic printhead at the end of a 5m multicore cable.

The cost of bits didn't matter much so I generated my sine wave with an AD DDS chip.

I used the ADC on an ST processor. The key to getting a good result, with the least calculation, is to sample synchronously with the sine wave - you need a minimum of 3 samples

per sine cycle but I used more (8 or 10 I think).

Because each amplitude measurement effectivley averages thousands of samples the 12 bit converter could still give more than 80dB dynamic range.

From your plots I think you are already sampling synchronously - it took a fair bit of juggling with settings on the processor timers and ADC to get the DDS synched up - it was clocked with a timer

pulse from the processor.

Will you post a schematic some time - that would be nice.

(One day I'll work out why the spelling checker doesn't work for me in E14 [View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-2b5ffff2-aad4-4a3b-8cf8-cc3028951117/contentimage_5F00_4027.png:16:16] - I think I've fixed all the typos)

RE: Pico Puffer

dougw — Tue, 10 Aug 2021 05:15:11 GMT

Cool application.

That kind of sensitivity will allow the system to detect a person walking by.

Is stray capacitance going to cause problems?