timing circuit advice

[nathanj99]

Hi

I am after a little advice on timing circuits. I am after a timing circuit to control the timings of the charge and discharge of a capacitor. I was going to use the 555 timer circuit from the SG, until I realised the timer starts running as soon as the main switch is thrown. It is independent of the speed of the wheel. So any change in rpm and the timings will have to be adjusted. Any Ideas of how this can be done with tieing the timing circuit into the actual wheel? I have attached a pic of the circuit I was going to use or see link below.

http://johnbedini.net/john34/Rad+monopole.jpg

Thanks

Nathan

[MarkE]

Hi

I am after a little advice on timing circuits. I am after a timing circuit to control the timings of the charge and discharge of a capacitor. I was going to use the 555 timer circuit from the SG, until I realised the timer starts running as soon as the main switch is thrown. It is independent of the speed of the wheel. So any change in rpm and the timings will have to be adjusted. Any Ideas of how this can be done with tieing the timing circuit into the actual wheel? I have attached a pic of the circuit I was going to use or see link below.

http://johnbedini.net/john34/Rad+monopole.jpg

Thanks

Nathan

If you want to make the pulse width inversely proportional to the wheel speed using analog circuits: then use a 555 or other monostable with a fixed width to generate a tachometer voltage, then buffer the tachometer voltage into a voltage to current source connected to the timing capacitor of a second 555 or other monostable.  Alternatively, you can just program an Arduino.

[nathanj99]

If you want to make the pulse width inversely proportional to the wheel speed using analog circuits: then use a 555 or other monostable with a fixed width to generate a tachometer voltage, then buffer the tachometer voltage into a voltage to current source connected to the timing capacitor of a second 555 or other monostable.  Alternatively, you can just program an Arduino.

Thanks Mark, although that did go a little over my head . Im trying to capture the bemf from the main pulse. I want to capture the bemf in a very small time frame and then pulse it back.

[MarkE]

If you want to put all the BEMF energy back into the power supply then you want a full H bridge.  The venerable L298 from ST Micro will work for up to 2A and comfortably into the 12V supply you have, but it needs four diodes.   It is over 30 years old so there are lots and lots of example circuits on the web.

[nathanj99]

Oh yes, I have briefly looked at the H bridge before. Do you think it's the right way to go in a OU machine? It looks like there could be a fair amount of wasted energy there?  How would you control the switching?