27/08/2009 Progress

EV Batteries

• Good news ! In the process of trying to work out how a 555 can better work with a PNP transistor (and after much experimenting on a breadboard) I found an excellent circuit here.
• Breadboarded the circuit (see below) and it works perfectly !

• Bad news ! I am going to have to create a new circuit board ... but this is also good, because next time around I will include headers for better wire connections. Not happy with the wires going into the box last time around.
• I have studied and think I understand the circuit now ... all except the diode.
• Have sent email to the author, and also created a thread on a circuits forum (here) to which I received a reply, that the diode seems only to be there to discharge the capacity on turning off power (which will not apply ... if ground is switched instead of positive).
• ...
• Finished first draft of the new circuit board for the controller.
• Put all components on the breadboard, and hooked them together. They work perfectly ... except that there wasn't quite enough current with 4 x 220ohm resistors before the first 12V zener. Taking down to 2 x 220 ohm resistors works perfectly. Will need to replace all with 100 ohm resistors (or similar).
• Also - didn't get to check the 75 ohm resistor in series with "stop" button (didn't have such a resistor).