[Open_electroporator] Timers, PWM, low-level MCU setup

[Nathan McCorkle]

On Wed, Mar 22, 2017 at 10:25 AM, John Griessen <john at cibolo.com> wrote:
> Hmmm... sounds like great news.  I was measuring 1800V with independent
> fairly calibrated instruments, not depending on the resistor chain, so maybe
> the machine
> can generate 11 kV...  but probably not, or the caps would have failed as
> they were rated 3 kV.

Yeah I was concerned and a bit scared I'd arc something in the coil,
or elsewhere as you suggested... before I get to zap any cells!

>
> Needs more verifying.  What load resistance at the cuvette contacts?  30
> kOhms?

33k 1/W


> The spikes on the leading edges suggest you have a light load on the cuvette
> contacts.
> the thicker trace that decays exponentially just after the spikes is a
> desirable, doing work, pulse shape.

I was actually thinking the long tail might be undesirable... in the
sense that it might be too long of an 'exposure time' for cells. It
sounds like we can control that by adding load (to dampen) or remove
load (to lengthen).

Maybe with the ADC, we can pre-measure the bacterial cuvette, then
with some MUXer or otherwise programmable variable resistor, set the
load as we desire. I have looked into programmable resistors before,
for setting Variable Gain Amplifiers feedback (and thus
amplification), but I don't seem to recall them being 'very cheap'.


>
> "Another video"  shows what looks like the same plateau of volts level.

Yeah it is pretty similar... main difference with second is that only
32 for width, versus the first video's 150.

My o-scope has ethernet, which I haven't explored in a few years since
I bought it. With that, I believe I can setup a completely automated
pulse and capture script, to enable us to make a shmoo plot of these
settings, etc.


> Are you using a 100X probe, or the resistor divider chain to measure volts?

the probes are set to 10X mode, using these:
Rigol RP2200 - http://www.alldaq.com/fileadmin/transfer/products/107216.pdf
and some cheap probes from-Amazon "2 X 100MHz Oscilloscope Clip Probes
with Accessory Kit"

> Have you found a clean low impedance pulse generator to observe with your
> probe
> so you can adjust out spikes due to probe compensation mismatch?

The scope has a low-kHz calibration hook, I will hook on later, adjust
as needed, and re-run.
The scope also has a built-in signal generator with a 50 Ohm mode...
that sounds low-impedance enough. The square wave should be able to go
into low MHz.

> The narrow
> spike
> peaks are probably fictitious volts.  The thick , (noisy), trace parts are
> probably all that is real.


Ok, cool :)

Something someone online asked was about that noise, any ideas we can
answer such questions with? (that don't require big-honkin
capacitors?)

Best,
-Nathan