No snow, no carol singers, no terrible TV.

BUT, I got the best present anyone could ever wish for.  A HAMEG HM604-2 oscilloscope!

Okay, possibly not everyone’s ideal Christmas gift, but it certainly was mine!

When I got back with it yesterday evening, I cleared some space for it (…OUT with the TV, DVD and FreeView box, thankYOU!..), then before I got totally carried away, I made some dinner, and sat down to think what my next steps would be with The Circuit.

I needed to see just what the input to the chopping FETs was -to see that the current was being switched properly by the PWM.  To do this, I needed a stable voltage input, so I’ve temporarily reverted back to using the power supply instead of the bike.

10% chopping.

10% chopping.

Here you can see the waveform of the input to the final chopping FETs set at 10%.  Now, these FET inputs are in effect ‘active low’ which means that where the signal dips below the majority of the line is where the FETs are switching for only 10% of the time.

The six ‘dips’ starting from the left you can see are where the FETs are switching ‘on’, allowing current through to the rest of the circuit.

Now, when you turn the voltage up a little, you see this:-

80% chopping.

80% chopping.

This shows the FETs switching at 80% of the duty cycle.

You can see from this that the majority of the line is ‘lower’, meaning that the FETs are switching on for longer.

Of course, voltage and current trigger levels need to be adjusted so the circuit comes on and off at ‘sensible’ times, but as you can see, its working!

I should just note that at this 80% switching, the meters on the power supply are reading approximately 15 volts with a current of 2 Amps flowing.  This proves to me that the battery is charging (…if it wasn’t, no current would be registering…), and the two switching FETs ‘have the chill taken off them’.  This is ‘Engineer Speak’ for getting warm, but not toasty: Nothing to worry about.

I’m due down at The Plots for 4.00 this afternoon, but will carry on with this ’til then.