Click here for a list of the parts required to build an SC129, v2.0, Digital I/O module.
Experienced builders please read the sections below about headers. Other than that there shouldn’t be any surprises to catch you out so just go ahead and assemble it.
I/O header
Digital input and output signals are available for external connection at P2. This can either be header pins, similar to those shown below, or a shrouded “box” header. The box header offers the benefit of being keyed to avoid a ribbon cable being connected the wrong way around.
Bus header
The PCB is designed to use a double row of header pins as the bus connector. You may wish to use a single row header to make the module height consistent with other modules that use single row headers, as explained here.
Getting started
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 circuit.
The picture below shows what a completed SC129 should look like.
IC sockets
Fit and solder the IC sockets (shown below in yellow)
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.
Resistor networks
Fit and solder the 8x100k resistor network RP1 (shown below in blue).
Fit and solder the 8x1k resistor networks RP2 and RP3 (shown below in green).
The 100k network will be marked 104 while the 1k network will be marked 102. If you want particularly bright lights you could fit 470R resistor packs instead of 1k resistor packs.
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.
Capacitors (100 nF)
Fit and solder the 100 nF cacacitors, C1 to C4.
These can be fitted either way around as they are not polarity dependent.
Header pins
Fit and solder the header pins.
P1 is usually a double row right-angled male header but with some pins removed.
Alternatively, you could fit a single row right-angled header.
This choice is explained here. The module functions the same in both cases.
P2 is usually a double row right-angled shrouded “box” header.
Digital input and output signals are available for external connection at P2. This can either be header pins or a shrouded “box” header. The box header offers the benefit of being keyed to avoid a ribbon cable being connected the wrong way around.
JP1 is a double row straight pins.
You could fit a right-angled male header here so that jumper shunts can be changed when the module is mounted in a backplane with other modules in front of it which would block access to a straight header.
Light Emitting Diodes (LEDs)
Fit and solder the orange LEDs (LED1 to LED8) and the red LEDs (LED9 to LED16).
It is important to fit the LEDs 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).
Capacitor (100uF)
Fit and solder capacitor C5.
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.
Quick Tests
Visually inspect the soldering for bad joints and shorts. Clean and inspect again.
Check for a short on the power supply tracks by measuring the resistance between IC U1 pin 20 and U1 pin 10 (indicated below in red). This should be an open circuit, not a short circuit. 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.
Integrated circuit
Insert the integrated circuits (ICs) into their sockets, taking care to insert them the right way around, as illustrated below. Be careful not to bend any legs over.
ICs are usually supplied with the legs slightly spread out making them difficult to insert. It is best to bend the two rows of legs so they are parallel before inserting them. Remember, these components can be damaged by static electricity so if possible earth yourself and the components while handling them.
Address select jumpers
Header JP1 is a male header with 2 rows of 8 pins. These are the 8 address select jumpers and are labelled with their bit numbers.
The module responds to input/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).
The default address for an RC2014 is zero (0x00). This is selected by having no jumper shunts fitted.
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.
You are now ready to give it a try.
Testing reset
Connect the Digital I/O module (SC129) to an RC2014 or compatible system and power up.
If your system has a working power on reset then none of the module’s LEDs should be on. If your system usually needs a manual reset then reset it now and check all the module’s LEDs are turned off.
If any of the output LEDs (LED1 to LED16) are turned on at reset, check for a problem around IC U2.
If any of the input LEDs (LED9 to LED16) are turned on at reset, check for a problem around IC U3.
Testing inputs
To test the inputs, simply connect each input pin on header P2, in turn, to 5 volts, as illustrated below. When the input is connected to 5 volts the LED should light. This test should work with or without IC U3 fitted.
If an input LED does not light, the most likely explanation is the LED has been fitted backwards.
The inputs can also be tested from BASIC or from the Small Computer Monitor (SCM). With the module’s address set to zero (no jumper shunts fitted), the input port can be displayed with the following commands.
From BASIC:
PRINT INP(0)
The result will be the input port value shown in decimal.
From SCM:
I 0
That’s the letter “I” and the number zero. The result will be the input port value shown in hexadecimal.
In both cases, the result should be zero if there are no external connections to header P2.
Testing outputs
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.
From BASIC:
OUT 0, 1
Where ‘1’ is the required decimal value to be written to the output port.
From SCM:
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 output signals can also be tested with a multimeter by measuring the voltage on each of the output bit pins in header P2.
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