Introduction
This modification allows full two analogue car racing on a PB-ProSH set-up. Special code has been written to enable a second PWM stream to be controlled by throttle number 2.
Additional to these modifications that automate separation of lane 1 from lane 2 at the powerbase, all links at lane changers and other Scalextric ancillaries will need to be cut. Actually only the right rail links need to be cut as the left rail remains as a common earth
This rates at my difficulty rating 9/10. Micro-soldering to the ends of tiny surface mount components is hazardous and extremely difficult. Getting everything into the space is also a bit of a squeeze. Note the relay used is only rated at 8 Amps, you can substitute something larger if you are expecting to have a very high continual current draw, but this was the only one that we got to fit inside the case. As all electronics go through a de-rating process then it should be good for bursts of current well above this without failing.
We mount it on veroboard or the heat transmission into the relay on soldering destroys the relay.
The chosen relay takes too much current for the PIC. It needs 80mA & a PIC output pin is only good for 25 mA. We have used an analogue transistor as an emitter follower. Base driven through the resistor 47 ohm, that's already on the board from pin 8 (RB0), collector to 5 Volts, emitter to coil, other side of coil to ground.
What do you need?
Parts needed for this are:
One piece of veroboard 36mm x 24mm – number of holes 14x8
One double acting two pole relay Farnell 8 Amp DPCO 5V coil. Part
number 109-4015
One transistor farnell 146-7866 npn to-92 bc338
Wires to suit
Dremel and ball cutter
Double sided carpet tape
Soldering iron, solder
Preparation
Disassemble base and top of your powerbase, to leave just the board and the track. To disconnect the display from the main board push out the locking black tab (white on some) and then pull out the flexi (noting for reassembly that the blue bit is uppermost.
Remove the two screws retaining your S-H board. Disconnect the wires on M1 and M2. Bend the board away from the processor to give access
Relay sub-assembly
Mill the verobard down the centre to split the tracks using your Dremel and ball cutter.
Identify the coil end of the relay – its the end with two pins rather than six. Mount the relay to the vero board centrally but leaving two whole rows of holes at the coil end. Solder it in place.
On the six pins, add a red wire to link the upper left to the lower right. This takes power so make sure it is a thick wire.
Now bend the legs on the transistor so that they are in line and the correct pitch to fit the veroboard
Fit to the veroboard. Flat side of the transistor closest to the relay. Other two legs are using the two rows of pins we left.
Beside the middle leg solder a blue wire
Beside the end pin solder a red wire
Beside the opposite teminal for the coil solder a black wire.
