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I've made a little detector for static electricity which works. I am trying to simulate it....but no go. What would be the input for static electricity? Background: I am building a tool for counting the number of times a hummingbird feeder is visited. Hummingbirds generate a little static so I am hoping my circuit can work as a sensor. The circuit works as it should but I can not simulate it. You can see my circuit as Static Detector by stephenp.

I would put a relay in parallel with the LED later to switch on the counter circuit. Any tips gratefully received.

Hi @stephenp, very interesting. It looks like you're making use of a JFET's gate directly as a static-senstive element.

Just curious: are you doing anything to bias the gate of J1?

Here's how I am interpreting your circuit -- let me know if this is correct:

At steady state (when there's no static), J1's $V_\text{gs} \approx 0$ and it conducts current into Q1's base. This causes Q1's collector voltage to drop, which turns OFF Q2 (and thus the LED is OFF).

When there is static (at least in one direction), J1's gate is pulled to pinch-off, which turns off Q1, and turns on Q2 and the LED.

Eventually J1's $V_\text{gs}$ discharges and J1 turns on again, turning on Q1 and turning off Q2 and the LED. (This time delay can probably be adjusted by adding a resistor between J1's gate and source.)

If that interpretation is correct, than it seems the simplest way to simulate it would be by adding a bit of voltage at J1's gate (i.e. V2 with the other end grounded).

A slightly more advanced way would be to use a switch to connect a voltage source, and then disconnect that voltage source, allowing it to discharge naturally.

Thanks --- your interpretation is correct and much clearer than I could have written!

Got it working thanks, with a voltage source between -3 and +3. Switches at -1. Put a 10K between gate and source. Your help appreciated.

First off, what an ingenious gadget!

An earlier comment by @mrobbins alerted me to something interesting: "When there is static (at least in one direction), J1's gate is pulled to pinch-off ..."

I tried to answer the question of how a positive pulse might produce a negative gate voltage. Some thoughts in the simulation ChargeDetection01 https://www.circuitlab.com/circuit/537ky266f569/chargedetection01/.

I'm aware that this might be pushing the boundary of what is on-topic, however, I've learned a lot about JFETS.

Thanks----I found that the 2n3819 needed too much fiddly bias. I switched to a J112 and it works much better. I cannot open your simulation.....CL blocks me. Did you make it public? I had assumed that static electricity would be negatively charged but frankly I haven't really worked it through. I am doing some real-world testing later to make sure those birds carry enough static. If you send me stephenpeplow34#gmail.com your email I can send you a photo. There has been quite a lot of research into HBs and static. My little circuit turns on a doorbell TX when static turns on the circuit. The doorbell RX picks this up and uses it to trigger a decade counter. The RX is inside my kitchen. I too have learned a huge amount about JFETs from doing this. Thanks!

Whoops! ChargeDetection01 https://www.circuitlab.com/circuit/537ky266f569/chargedetection01/ now public.

In the Description is a reference to a biology paper on charged Hummingbirds - very interesting if you've not already seen it.