SC148 is a power supply module designed for the RC2014 bus.

This module supplies power to the RC2014 bus.

The power input must be from a regulated 5 volt D.C. power supply that can provide at least 1 ampere (1000 mA) of current. The 5-volt (nominal) input should be within the range of 4.75 to 5.25 volts. The switched 5-volt output can 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 the onboard reset switch (push button), a reset switch on the backplane, or an external reset switch connected to the onboard pin header. A voltage supervisor and reset device is also included, which provides a reliable power-on reset.

The main features of this design are:

• Voltage input is 5 volts (4.75 to 5.25) at up to 1 amp
• Power input via 2.1mm power jack or screw terminals
• On/Off toggle switch
• Power indicator LED
• 5-volt output via screw terminals and header pins
• Front-facing reset button
• Reset indicator LED
• Voltage supervisor and reset device

Jumpers

JP1 (shown below in red) can either be constructed using header pins and a jumper shunt, or a soldered link (for greater reliability). If header pins are used then a jumper shunt must be fitted. This jumper shunt or soldered link 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 shunt or soldered link. The left-hand position selects ON = Down, while the right-hand position selected ON = Up.

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 enabled in your system.

Input supply

The module is designed for a voltage input of between 4.95 and 5.25 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 silkscreen on the circuit board. There 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 4.75 to 5.25 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 of the 5-volt switched 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 enabled, it should also light for about half a second after switching on.

External reset switch

An external reset switch can be connected to the pin header, P2, 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.