• 8 channel logic-level signal monitor
• Pulse-stretching to capture quick edges
• Analog input on up to 6 of the channels
• New PWM duty-cycle measurement
• Up to 2 debounced button outputs
• Ideal for breadboard mounting
• 3V to 5V operation
• Firmware-updatable

What is it?

This small board contains a 1-inch OLED screen and provides monitoring of the logic level of up to 8 input channels. Each channel is shown individually on the screen by two "virtual LEDs" - one to show a high logic level, the other low. Each virtual LED can also light dimly to show short edge-transitions, such as might occur on a serial connection or bus. It is supplied fully constructed and programmed, ready to plug straight into a breadboard to begin debugging your project.

Three buttons provide a simple configuration menu on the display, allowing the user to configure each channel with optional pull-up, or to switch the channel into duty-cycle, analog, or button mode.

In duty-cycle mode, a channel will show a bar-graph indicating the relative ratio of high vs low states in recent sampling history. The size of the bar is low-pass filtered to show a relatively stable reading suitable for indicating things like PWM outputs intended to drive an LED - the bar graph indicates a reasonable approximation to the apparent brightness the LED would have.

In analog mode, a channel will instead show a bar-graph reading the analog voltage level present on the pin, as a fraction of the supply voltage. Due to limitations of the microcontroller used, only 6 of the 8 channels are analog-capable. The first two channels are digital-only.

In button mode, the channel becomes an output whose logic state is controlled by one of the buttons to the side of the display. Up to two channels may be in button mode at any time. Each button can operate in normally-low, normally-high, or toggle mode.

As well as the 8 input or output channels, the board requires power and ground connections. These are all provided on a 10 way 0.1" pin header, which is ideal for plugging directly into a breadboard, to act as a development and debugging aid for working on digital circuits. It can be powered on anything between 3V and 5V.

An extra pin is provided to allow the onboard firmware to be updated or replaced.

Instructions

Initially, all 8 channels are configured as digital logic inputs with pull-ups enabled. Each will display as two virtual LEDs on the display - one to show high state (the top LED) and one to show low state (the bottom LED). Each LED will also light in a half-shaded pattern to indicate a fast edge transition such as a clock or interrupt pulse.

The three buttons on the right side of the display are used to operate the setup menu. Pressing the top "Menu/OK" button will enter the setup menu. From here the "Up" and "Down" buttons will navigate the choices; pressing the "Menu/OK" button will activate the choice. A long press on the "Menu/OK" button will exit the menu and return to the main screen.

Why did you make it?

I originally made this as a better replacement of the breadboard-mounted set of LEDs style of debugging tool, of which I have several. I found I needed some pulse-stretching logic to capture quick edges of serial buses. The buttons and analog-read abilities came largely "for free" because of the microcontroller and board arrangement being used here.

What makes it special?

While simple sets of LEDs on a breadboard work fine for simple cases, their inability to pulse-stretch makes them less useful for working on serial bus or other high-speed digital systems. Simple breadboarded buttons often require additional debounce logic being added which is sometimes awkward when doing a quick development or debugging task not directly part of the main project; having a debounced button available on the breadboard would be handy. This tool combines a handy set of logic monitoring features with some button outputs in a conveniently small board area that can be mounted vertically on a breadboard, minimising the space required. While fancier logic analysers certainly exist, they are almost always PC-based and require some support software on the machine. This tool is entirely self-contained, showing outputs on its own display.