Click here for a list of the parts required to build an SC135, v1.0, digital output module.
Experienced builders can just go ahead and populate the board. There shouldn’t be any surprises to catch you out.
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 SC135, digital output module should look like.
Fit and solder the bus header pins P1 (shown below in red).
Fit and solder the IC sockets U1 and U2.
Be sure to fit them with the notch matching the legend on the circuit board, so you do not end up fitting the IC the wrong way around too.
Capacitors 100 nF (0.1 µF)
Fit and solder 100nF capacitors C1 and C2.
These capacitors can be fitted either way around, as they are 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.
Fit and solder the 8x10k resistor network RP1.
The 10k network will be marked 103.
Take care to fit the resistor network the correct way around. Pin 1 is usually marked with a dot. This end is indicated on the PCB and on the illustration below.
Header (double row)
Address selection is via jumper shunts fitted to a double row of header pins. These can either be straight pins or angled pins. Angled pins stick out above the module allowing easy access to the jumper shunts when the module is fitted to a backplane. Straight pins look neater but do not allow the address to be changed when the module is fitted in a backplane with another module immediately in front of it.
Fit and solder double row angled header pins or double row straight pins in position P4 (renamed JP1 on later boards).
Header (angled, single row)
Fit and solder the single row angled header pins, P2 and P3.
You can either fit P2 and P3 as two separate strips, a 10-pin strip and a 2-pin strip, or you can use a 13-pin strip by removing the 11th pin. Unwanted pins can easily be pulled out of the plastic with a small pair of pliers. Cutting a long strip into shorter pieces can be done with a pair of wire cutters.
Repeat the check made earlier for a short on the power supply tracks. Connect the meter probes to IC U1 pin 20 (shown below in red) and U1 pin 10 (shown in green). 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 100 kΩ (100000 ohms) is acceptable.
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.
If all the above tests check out okay, insert the integrated circuits into their sockets. Take care to insert them the right way around, as illustrated below. Be careful not to bend any legs over.
Address select jumpers
Header P4 (later renamed JP1) is a block of header pins with 2 rows of 8 pins. These are the 8 address select jumpers and are labelled with their bit numbers.
The module responds to output addresses matching the address set with these jumpers. When a jumper shunt is fitted, that bit must be a 1 (high voltage). When the shunt is not fitted, that bit must be a 0 (low voltage).
If, for example, you wish to set the module to address 32 decimal, which is hexadecimal 20 or binary 00100000, then fit a single jumper shunt to bit 5.
The least significant address bit (bit 0) does not do anything with this design, but has been included as a place holder for consistency with other modules. You may wish to cut off the pins for bit 0 as a reminder that bit 0 is not used.
You are now ready to give it a try.
Connect the digital output module (SC135) to an RC2014 or compatible system and power up.
If your system has a working power on reset then none of the module’s outputs should be on. If your system usually needs a manual reset then reset it now and check all the module’s outputs are turned off.
If any of the outputs are turned on at reset, check for a problem around IC U2.
The outputs can be tested from BASIC or from the Small Computer Monitor. With the module’s address set to zero (no jumper shunts fitted) the output port can be written to with the following commands.
OUT 0, 1
Where ‘1’ is the required decimal value to be written to the output port.
O 0 1
Where ‘1’ is the required hexadecimal value to be written to the output port.
Note: That’s the letter “O” and the numbers zero and one.
The SC135 User Guide can be found here.
Other information about SC135 can be found here.