The G-EDM is one of the few DIY wire edm machines that not only comes with the pulse electronics and sensing circuits but also provides it's own firmware.

Making the firmware was and still is the core of the project while the hardware was left as it is for most of the time. It worked very well and there was no reason to look at the hardware much.

Recently I took some time to take a very close look at the sensing circuit and it turned out that the circuit does not fully maximize the potential it has.

I spend countless hours analyzing all aspects of it and test different things.

Many of the tiny discharges where not captured by the current sensing. Based on the information available this is not a big issue and capturing a single static discharge would require very expensive hardware and to run a wire EDM it is not needed as long as the firmware is well programmed.

But that doesn't mean it shouldn't be tried. And while working on the existing unit it turned out that by changing some resistor values and capacitors the sensitivity heavily increased making the current sensing section reacting much faster to even small discharges.

The current channel had three 100pf capacitors in total. One between the shunt inputs, one at the low pass filter and another one on the opamp feedback that controls the linear optocoupler.

I removed the 100pf capacitor on the input and changed the capacitor on the low pass filter stage and also the one on the optocoupler. This improved the reaction by a lot already.

Another thing is the gain of the low pass stage. It was using a zero Ohm gain resistor making it a unity gain opamp. Tiny jumping sparks that are like static discharges create very tiny currents and a very fast. They don't create much feedback but they can indicate reaching the discharge gap distance where sparks start to jump and therefore it would be nice to capture at least some more of them and therefore I changed the gain of the low pass filter. And to make the circuit faster the LM358 was replaced by an OPA2350. The current limiting resistor on the optocoupler was also changed to a lower value.

Those changes can be done to existing boards. There is no change except the component values.

Another thing is voltage sensing. The current way is to monitor the powe rinput provided by the DPM or DPH and use a drop in voltage as a hard short circuit indicator. Once the current exceeds what is set on the DPM/DPH it will start to switch and create a voltage drop and it is almost always are true short circuit then.

But other then that the voltage channel did not provide much usable information. By connecting the input of the voltage at the Mosfet drain instead of the power input it creates a linear voltage feedback. The nature of a low side switch makes it a little tricky to work with as the voltage drops to zero while the Mosfet is conducting in the ON phase but this is still doable. The conductivity of the water, size of electrode also heavily impact the feedback. The recent developments are very promising and this little video shows how the feedback reacts now.