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1. OVERVIEW
The I/O board contains various input and output devices, for the purpose of experimenting with simple digital circuits. It is designed to fit directly onto a breadboard (prototyping board) and features a logic probe that can aid in debugging and a UART serial interface for communication with other devices.
FIGURE 1 - I/O BOARD
The board is powered from a single USB connection and features current-sense your designs.
circuitry that detects short circuits and protects
I/O BOARD USER MANUAL
1. USB Connector
2. Power LED
3. Power Switch
4. 7-Segment Display
5. Switches
6. LEDs
7. Buttons
8. 9. 10. 11. 12. 13. 14.
UART Transmit/Receive LEDs Logic Probe Indicator LEDs Fault LED
VCC / GND Headers
I/O Device Headers Auxiliary Power Connector High Current Mode Jumper
FIGURE 2 - BOARD OVERVIEW
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2. SETUP
To begin using the I/O board, first insert it into a breadboard as shown in Figure 3. Take care to align the downward facing headers with the appropriate holes in the breadboard.
NOTE: If aligned correctly, the I/O board should not require excessive force to insert it into the breadboard.
FIGURE 3 - I/O BOARD INSERTED IN BREADBOARD
Connect a micro-USB cable to the connector on the top-left corner of the board.
FIGURE 4 - USB CONNECTION
DO NOT STORE THE BOARD WITH THE USB CABLE ATTACHED - THIS MAY CAUSE THE USB CONNECTOR TO BREAK OFF!!
Turn on the I/O board by sliding the PWR switch up into the ON position – the red power LED should illuminate.
Check to see that the orange FAULT LED does not light up. If it does, turn the power off immediately by sliding the PWR switch down into the OFF position – see Section 3: Fault LED.
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3. FAULT LED
The I/O board uses a current-limited power switch to protect itself and any circuits that it powers from harm due to short- circuits. In the case of a short circuit, the orange FAULT LED will be illuminated.
FIGURE 5 - FAULT LED
If the FAULT LED is on, immediately turn the power off to the board by sliding the PWR switch down into the OFF position.
Check your design for short circuits before returning power to the board.
WARNING! In the case of a short circuit, the current-limiting switch may become extremely hot!
4. SWITCHES, LEDS, BUTTONS
The I/O devices are all accessible via the breadboard holes directly above/below the relevant labels printed on the I/O board
(see Figure 6 - I/O Device Labels). The switches are labelled S0 ... S7; the LEDs L0 ... L7; and the buttons B0 ... B3.
FIGURE 6 - I/O DEVICE LABELS
These I/O devices can be connected to other circuit elements by connecting a wire from the column of terminals in the breadboard above/below the relevant label. An example of this is shown in Figure 7 - Example Connection, where the switch S0 is connected to pin 13 of an external device and the LED L0 is connected to pin 11.
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5. LOGIC PROBE
FIGURE 7 - EXAMPLE CONNECTION
The Logic Probe can be used to analyse the logic state of points within a digital circuit. It is used by attaching a wire to the column of terminals above the PR label (see Figure 8 - Logic Probe). The other end of this wire can then be touched to other points around a circuit and the HI / LO LEDs will indicate the logical state at that point in the circuit.
FIGURE 8 - LOGIC PROBE
A logic probe is a simple, yet useful tool for troubleshooting digital circuits. When used as part of a well thought-out debugging strategy it can greatly speed up the process of finding and fixing errors. As circuits increase in complexity, so does the necessity to have a clear strategy in mind when debugging them, as probing random points in a large circuit rarely reveals the location of errors.
Suggested Troubleshooting Strategy
1. Check that the FAULT light is not on, indicating a short-circuit
2. Probe the VCC and GND connections at every device in your circuit to ensure each is powered correctly
3. Start at the inputs to your circuit, probe the inputs to verify their logical state; move logically through the circuit from input
to output – a pen and paper will help here (write down the expected state at each point and then verify this state using the logic probe – a schematic and a truth table are great for this!)
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This strategy is not a fool-proof guide to solving any problems within a circuit, but it is a useful starting point to begin developing your own approach. The key to any successful debugging strategy is to assume nothing, know what to expect before you actually begin testing and have a plan!
Electrical Characteristics
VCC
GND Logic High Logic Low
5V
0V
> 3.5V < 1.5V
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