While parts for the new combustor were being sourced, there were a few other things that could be worked on. One of those projects was the computer relay module. The relay module is used to switch current on and off to the many pumps, fans, and other gear needed to run the bike. As this is another soldering project, I have just included pictures of the completed module.

Please excuse the quality of the pictures. For some reason that is completely unknown to me, every time I try to get a good picture of these boards the pictures are a bit odd looking. If anyone has a digital camera that they would like to donate to improve the quality of the pictures, please let me know.

Relay module description map

The relay module above is made up of few parts, and is designed to be easily repaired and installed in the bike. The few parts on the board are as follows:

1) Terminal strip for making power and output connections
2) Ribbon cable header for instructions from the stamp or LCD
3) Darlington array chip (ULN2803A)
4) Red LED power indicator
5) Green LED relay state indicator
6) 10 AMP relay

Relay module connected to stamp carrier board on right

The relay module connects to the stamp carrier board using a 10 pin ribbon cable. The cable uses 8 of the conductors to send signals to the board to switch the relays on and off. The cable can also be connected to the output of the LCD screen. The LCD has a 10 pin connector which can send the on off signals to the module, and effectively gives 8 more outputs to the ECU, as the 16 I/Os on the basic stamp are all being used by the various sensors.

The module powered up

As you can see in the image above, the LEDs indicate which relays are active and passing current. The red LED lights when power is supplied to the board, and the green LEDs light when their corresponding relays are turned on. The LEDs are helpful for finding problems with the electrical system should the need arise.

The module completely energized

The relay board allows the many pumps and support devices on the motorcycle to be turned on and off by the ECU. As the ECU is a 5 volt device and the pumps, etc. are all 12 volt devices, some sort of switching device was mandatory.

Warning! Electronics explanation below. But it is easy to follow.

The basic stamp can only supply a very small amount of current to switch devices, so the relays will be used to switch the higher amperage loads. Unfortunately, the stamp is under powered to even switch all of the relays at the same time. This is where the darlington array comes in. The darlington array is a transistor circuit that gives the stamp more muscle. By supplying a very small current to one of the 8 input pins on the darlington, the corresponding output pin can supply enough current to power a relay and LED.

The transistors in the darlington are simple devices. There is a common positive ground, and an input and output. When a negative current is passed to the input (or collector) the power output (or emitter) is switched to the on state and emits a negative voltage. The positive ground is called the base. This type of transistor is called a NPN transistor, as it uses a negative input and output, and a positive ground. So negative, positive, negative is where we get the NPN. There are also PNP transistors which work exactly the opposite for switching positive current with a negtive ground.

Now that we have a way to power the relay, they can be used to power the 12 volt devices. When power is supplied to 2 terminals on the relay, a small electromagnet pulls down a switch inside. The switch is connected to 2 more pins on the relay which can be used to power any load up to the rating of the relay. The relays on the module can switch loads of up to 10 amps each. The highest load of any item on the bike will be the pumps. The pumps use about 7 amps, so the relays will be suitable for switching current to them.

Basically, at this point we are using both the relays and darlington array much like levers. We use the leverage of the darlington to help the stamp be able to operate the relays, and the relays leverage the switching we need for the higher voltage and currents to the pumps and other accessories.

One problem exists when using relays with sensitive electronics like the stamp. When a relay is de-energized and the contacts open, a small power spike is generated. The power spike is caused by the magnet now being open and the switch moving away. In essence, it becomes a small generator with a moving magnet and a coil winding. Although the switch that is pulled by the electromagnet is not a magnet itself, it does retain a bit of magnetism for a brief moment when it is first released. This magnetism moving near the coil generates the spike. This spike can now move back towards the device which normally powers the relay and cause a current spike which can damage it. Once again, the darlington saves the day. It contains a tiny diode on each of its 8 switch circuits that acts as a protection device. Diodes allow current to pass in only one direction, and block it in the other direction. Since our current spike is moving backwards, it is now stopped in its tracks by the diode.

Now that we have all of that sorted out, we have a very reliable means to switch high amp loads using the very tiny output current from the stamp. The loads will be pumps, fans, ignition modules, solenoid valves, and lots more. The relay module fits right into the ECU enclosure and is designed to mount beneath the stamp module using metal standoffs that keep them separated.

I hope that this has been a little interesting and informative. Keep checking in as more updates will be coming soon. As always, thanks for reading, and for making the site what it is today. We appreciate your support.

Russ W. Moore
Bad Brothers Racing

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