Arduino Monitor/Tester

The reason for this little gadget is that although it is possible to monitor a lot of things through the serial interface, there is still nothing as good as seeing the actual signals on a “lamp” display. Many years of experience with electronics and automation have tought me that it is a very bad idea to monitor something through the same “channel” that you suspect to be faulty. In the development of various Mega and Due controllers I have had invaluable help of my “Arduino Monitor/Tester” with LEDs on all I/O’s. In addition to the indicators I incorporated various other output possibilities together with even a few different inputs. The features are the following:

  • One LED for every single input or output
  • Can be used with Due (target), Mega, Uno, etc.
  • Fit with my “Mega Shield”, another universal I/O board
  • Power taken from Arduino 5V output
  • Selectable 5V-3V input modes (for Due operation)
  • Voltage for steppermotor output can be selected between 5V and Vin
  • Monitor-load-resistance on any pin is 10 kohm or higher
  • LED intensity is proportional to pin voltage or duty cycle
  • IC-sockets and Arduino pins are all gold plated 🙂
  • Built-in inputs and outputs for testing new ideas:
    • One pushbutton (P) digital input
    • One toggle switch (T) digital input
    • Two potentiometer (1, 2) analog inputs
    • 4 outputs also connected to HEX-display (eg.: for program state indication)
    • Very small moving coil voltmeter on PWM output (from old tape-recorder :-))
    • Piezo loudspeaker on PWM output
    • 4 open-drain MOSFET outputs, incl. flyback diodes (for small stepper)
    • One opto-isolated digital input
    • One opto-isolated digital output (not for 230 VAC)
    • One direct analog input via miniature LEMO coax connector
    • One direct digital I/O/PWM via miniature LEMO coax connector
    • One reed-relay (no coil) to digital input
    • One mercury shake alarm to digital input
    • One TMP36 temperature sensor to analog input
    • One electret-microphone to analog input via op-amp (gain 100)
    • One NTC, linearized, to analog input
    • One LDR to analog input
  • All inputs and outputs can be made passive to enable inputs from other external sources
  • LED’s grouped in 16 for analog I/O, 14 for digital I/O/PWM, 8 for digital I/O/Tx/Rx and 32 digital I/O. In total 70 LEDs
  • All LEDs are very high efficiency white SMD types, with coloured film on top according to the group

This is how the front panel looks now, with all indicating text and numbers. As much as possible information is written on the front panel. This is a bit tricky, since some of the pins assignment differ between Mega and Due. The thing on the left side is the shake-contact:

The front panel consists of a sandwich of two pieces of transparent acrylic, a little longer than a MEGA board, and the same width. Between the acrylic pieces is a layer of semi transparent PCB-layout-“paper” (2,54 mm module), the type we used many years ago for taping up PCB lay-outs. The text is made with so-called “Letraset” letters that you transfer by rubbing each one of from a sheet with a collection of letters. All in all very old-school 🙂

The top photo shows how the various components are places, and maybe you can also spot that everything is hand-wired using soldered wirewrap wire. Below you can see the backside of the Monitor/Tester and all the pins that will go into headers on Arduino Mega/Due. You can also spot the jumpers for disconnecting all built-in analog inputs, and the selector for 5V-3.3V. A small piece of insulating film is placed where there is a risk that the large USB-connector (Uno/Mega) will touch. At the bottom of the picture you see the piezo-speaker, electret-microphone and two Lemo connectors:

Below you can see the separate compartment with the two LEMO connectors, TMP36 and NTC temperature sensors, and a blue LED indicator for 5V:

NOTE: The LEDs cathode reference is adjusted down to approx. -2V: LED will light up when pin voltage goes positive. The cathode reference is divided into one for analog and one for digital, and both can be adjusted . The small white LEDs from Osram (DURIS E3, type InGaN) are fabulous. In the top photo you can see how I mounted them. With a current of only 0.5 mA they will produce more that enough light for the monitor purpose. This means that I only have to load the inputs and outputs with 10 kohm. Click here to see the .pdf schematic: Monitor-Tester