Click here for a list of the parts required to build an SC142, v1.0, power supply module.
Experienced builders can just go ahead and populate the board. There shouldn’t be any surprises to catch you out.
Introduction
This guide assumes you are familiar with assembling circuit boards, soldering, and cleaning. If not, it is recommended you read some of the guides on the internet before continuing.
First check you have all the required components, as listed in the parts list.
Before assembling it is worth visually inspecting the circuit board for anything that looks out of place, such as mechanical damage or apparent manufacturing defects.
If you have a multimeter that measures resistance or has a continuity test function, check there is not a short on the power supply tracks. Connect the probes to each terminal of one of the capacitors, such as C1. This should be an open circuit, not a short.
The picture below shows what a completed SC142, power supply module should look like.
Resistor 1k
Fit and solder the 1k resistors, R1 and R2 (shown below in red).
Resistors can be fitted either way around, as they are not polarity dependent.
Resistor 4k7
Fit and solder the 4k7 resistor, R3.
Diode 1N4001
Fit and solder the 1N4001 diode, D1.
Diodes must be fitted the correct way around. The light coloured band at one end of the diode must be fitted into the circuit board at the end indicated by the silkscreen.
Bus connector
Fit and solder the bus header pins P1.
Capacitor 100 nF (0.1 µF)
Fit and solder capacitor, C3.
This capacitor can be fitted either way around, as it is not polarity dependent.
The exact value of this component is not critical. The use of very cheap capacitors within the range of about 30 to 200 nF is acceptable.
Capacitor 1 nF
Fit and solder capacitor, C4.
This capacitor can be fitted either way around, as it is not polarity dependent.
The exact value of this component is not critical. The use of very cheap capacitors within the range of about 0.5 to 10 nF is acceptable.
Capacitor 100 µF
Fit and solder capacitors, C1 and C2.
It is important to fit this capacitor the right way around. The negative terminal is indicated with a ‘minus’ sign, as illustrated to the right. The negative terminal also has a shorter lead.
The silkscreen has a plus sign for the positive terminal and a hashed area for the negative terminal
Toggle switch
Fit and solder the toggle switch, SW1.
Light Emitting Diode (LED)
Fit and solder the LED1 (green) and LED2 (red).
It is important to fit the LED the correct way around. LEDs usually have a small flat side to indicate the cathode (the negative end). This should be positioned to match the flat side shown on the circuit board (illustrated to the right). Also, the cathode pin on the LED is usually shorter than the other pin (the Anode).
Reset switch
Fit and solder the reset switch, SW2.
Voltage regulator 7805
Fit and solder the 7805 voltage regulator, U1.
Bend the legs such that the hole in the heatsink part of the regulator lines up with the hole in the printed circuit board. Bolt the regulator in place with an M3.5 nut and bolt, then solder the pins.
Headers (straight, single row)
Fit and solder the pin headers JP1, JP2, P3, and P4.
JP1 is a 3-pin strip, whilst the others are 2-pin strips.
These header pins may need to be cut from longer strips using wire cutters to cut the plastic.
You can make JP2, P3, and P4 from one strip with some pins pulled out of the plastic strip. This makes it easier to keep the three groups in a neat straight row.
Power connectors
Fit and solder the 2.1 mm power jack socket, J1.
Fit and solder the two screw terminal blocks, J2 and J3.
Ensure the wire entry holes face the edge of the PCB.
Voltage supervisor and reset
Fit and solder the DS1233 voltage supervisor and reset device, U2.
This device must be fitted the correct way around. Match the shape of the device to the legend on the circuit board.
It is necessary to spread the legs of the device to match the hole spacing on the circuit board. Do this gently so as to avoid straining the legs where they enter the plastic casing. DO not press the component hard into the board as this will also strain the legs.
Quick Tests
Repeat the check made earlier for a short on the power supply tracks. Connect the meter probes to the terminals of J2. This should be an open circuit, not a short. If you are using a digital meter set to measure resistance it will likely take a few seconds for the reading to stabilise as there are now capacitors on the power lines. A reading of more than 100k Ω (100000 ohms) is acceptable. Repeat with the toggle switch, SW1, in the other position.
Check the resistance between the two contacts of screw terminal J3. This should be at least 1000 ohms.
Inspection
Remove any solder ‘splats’ with a brush, such as an old toothbrush.
Visually inspect the soldering for dry joints and shorts.
Clean the flux off with suitable cleaning materials.
Visually inspect again.
Getting Started
A jumper shunt will need to be fitted to JP1 before the module can be used. The jumper shunt can be in either position as it just determines the polarity of the on/off switch, SW1, which will be either up for on, or down for on.
A jumper shunt on JP2 is optional, but leave it off for now. This jumper enables the voltage supervisor and reset device, U2.
Connect a suitable 8 to 15-volt supply to either J1 or J2. The green power LED should light when the on/off switch, SW1, is in the on position. The red reset LED should be off. Check the voltage at J3 is between 4.75 and 5.25 volts. If it is outside this range, check the voltage at J2 is between 8 and 15 volts. Next look for a problem around the voltage regulator, U1.
Once a good 5 volt supply is known to be available, check the red reset LED comes on when the reset button is pressed and goes off when the reset button is released.
Fit a jumper shunt to JP2. At turn on the red LED should now light for about half a second before turning on. This indicates the power-up reset is working correctly.
The SC142 User Guide can be found here.
Other information about SC142 can be found here.
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