Breadboard Gadgets

Here are some handy little boards that plug directly into a solderless breadboard and can be a great help for experiments with digital circuitry.

• ByteHex: Examine an 8-bit data bus, in hex, with numerous latching options.
• ByteDisplay: Similar to above but with 8 discrete LEDs. No microcontroller.
• ByteSwitch: 8-bit DIP switch with pull-up/down resistors.
• ClockGen: A pulse generator that produces a clock up to 1MHz with an adjustable duty cycle. Generates RESET pulses as well.

Fabbing the boards

Board dimensions are as follows:

• ByteHex: 25.4mm x 20.32mm
• ByteDisplay: 23.4mm x 20.32mm
• ByteSwitch: 23.4mm x 20.32mm
• ClockGen: 32.2mm x 20.32mm

They are all 2-layer designs. Fab them with your favorite color scheme.

Fab files may be found in each board's subdirectory in this repository.

BOMs are the CSV files in each board's subdirectory. Note that jellybean parts like resistors, capacitors, and LEDs have not been assigned Mouser part numbers. Feel free to pull from your junk box.

ClockGen uses super cute little trimmer potentiometers with knobs. The listed Mouser part number is quite expensive, so consider using this part from Spark Fun instead.

Building Firmware

The ByteHex and ClockGen boards have an ATMega328PB microcontroller. The code is meant to run without a bootloader and can be built from the command line if you have installed avr-gcc and avrdude.

make
make fuses
make prog

Note that the avrdude command lines in the makefile are hard-coded for the usbtiny programmer. You'll want to change that if you have another type of AVR programmer.

The MCU is new enough that your version of avr-gcc and avrdude may not support it yet, see here for instructions on how to fix that.

The bottom of each board has a standard 6-pin AVR programming header as a surface mount footprint. Since you only need to program it once, you could plug a header into the programmer's cable and physically push it up against the board, or you could temporarily tack-solder it in place. You can't really leave the header in place because it may interfere mechanically when you try to plug the board into a breadboard.

Using the boards

ClockGen

Adjust the frequency with the upper potentiometer. The lower potentiometer sets the duty cycle. When you set the duty cycle, the percent value will temporarily appear on the display.

The frequency range is set by the knob marked 0, 1, 2, and 3. These settings correspond with the following ranges:

Range	Frequencies
0	1 to 99Hz
1	100Hz to 999Hz
2	1KHz to 99KHz
3	100KHz to 999KHz

The rightmost decimal point will light up when the board is generating a reset pulse. The pulse period can be adjusted in the code by changing RESET_DELAY, and the reset threshold voltage is set in the code by VCC_THRESHOLD.

ByteHex

Plug the trigger signal into the TRIG jack on the board, or leave it unconnected and set switch 3 to L to display the instantaneous digital value.

There are four configuration switches:

Switch	Function
1 (6/9)	Right-side up (up) or upside-down (down) display
2 (R/F)	Trigger on rising (up) or falling (down) edge
3 (L/E)	Level sensitive (up) or edge-triggered (down)
4 (N/S)	Normal mode (up) or single-shot trigger mode (down)

The upside-down display is useful if you plug the board into the left side of a breadboard.

The level sensitive mode turns the device into a transparent latch when the trigger input is high (R) or low (F), depending on switch 2.

Single-shot trigger mode captures a single trigger event, freezing the display until you cycle power or change the trigger mode back to normal. This lets you capture a single data byte, something like a simple digital oscilloscope.

ByteSwitch

This design can be used in a variety of different ways.

• Tie VIN to your 5V rail and GND to ground. Switch ON=logic low.
• Tie VIN to ground and GND to 5V. Switch ON=logic high.
• Use as a miniature resistor twiddle box by leaving the header unconnected and jumpering VIN and GND to your circuit. How can you optimize the values of the resistors?

ByteDisplay

With the latch input unconnected, the board will drive the LEDs according to the logic levels present on the inputs (transparent latch). You can latch the inputs by connecting a pulse source to the latch input. When the latch input is low, the contents are retained from the last time the latch input was high.

Licensing

This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License. See https://creativecommons.org/licenses/by-sa/4.0/.