SC142 is a power supply module designed for the RC2014 bus.

This module supplies power to the RC2014 bus. The input is from 8 to 15 volts (D.C.) at a maximum of 1 ampere. The module contains a voltage regulator to provide the RC2014 bus with a 5 volt 1 ampere supply. This 5 volt supply can also be used to power external devices from the onboard screw terminal and pin header.

The module also provides a reset signal to the RC2014 bus. This signal is generated from a reset button, or external reset switch connected the onboard pin header. A voltage supervisor and reset device is also included, which can be enabled with a jumper shunt (JP2).

Jumpers

JP1 (shown below in red) must have a jumper shunt fitted. This jumper selects the polarity of the on/off switch, SW1. The convention for ON varies from country to country, with some using UP for ON and others using DOWN for ON. Select your preference with this jumper.

JP2 (shown below in green) enables the voltage supervisor (U2). This device holds the processor in reset if the voltage is below about 4.7 volts. Fit a jumper shunt here to enable the voltage supervisor, or remove it to disable the supervisor. If the system stays in reset, try disabling the supervisor.

Some other modules also include a voltage supervisor. You should only have one supervisor in enabled in your system.

Input supply

The module is designed for a voltage input of between 8 and 15 volts D.C. at a maximum of 1 ampere (1000 mA). It is important to connect this supply the correct way around, as indicated by the silk screen on the circuit board. There are are two input connectors, as illustrated below. Either can be used. One is for a power ‘barrel’ style jack plug, which has a 2.1mm centre pin (positive 8 to 15 volts).

Output supply

In addition to supplying 5 volts to the backplane through the bus pins, illustrated below in green, the module also has connections to power external devices. The two connectors, J3 and P3, provide 5 volts out.

Light Emitting Diodes (LEDs)

LED1 indicates the presence on the 5 volt regulated supply. With a suitable supply connected to one of the power inputs and the on/off switch in the ON position, this LED should be ON.

LED2 indicates the bus RESET signal is low. ie. the system is held in reset. This LED should light when the reset button is pressed. If the voltage supervisor is enable, it should also light for about half a second after switch on.

External reset switch

An external reset switch can be connected to the pin header, P4, indicated below. This might be useful if you wish to put your system in a box or position it where the onboard reset button can not easily be reached. A simple momentary action, normally open, switch is all that is required.

Troubleshooting

If the reset LED stays on, the processor will not run as it is in reset. Try disabling the voltage supervisor by removing the jumper shunt on JP2. The voltage supervisor will hold the RESET signal low if the bus supply voltage is below about 4.7 volts. If the problem persists check the reset switch is working. The easiest way to do this is to unplug this module from the backplane and connect a suitable input supply. The reset LED should only be ON when the reset button is pressed.