I wanted a board that shows the state of all I/O pins on LEDs with all of these properties….
- Works for Digital Input, Output, and Input Pullup
- Pushbutton to drive the pin high, very weak pulldown (much weaker than on-chip pullup)
- Works for analog pins (thumbwheel pot), but also works when the same pin is used for digital
- LED shows actual analog level – LED current should be linear to actual voltage
- LED current does not interfere with analog voltage
- LED does not interfere with weak signals, or input pullup or pulldown
- Inexpensive – under $0.50 per pin – many parts are ok, as long as they’re cheap!
I realize this is probably excessive design for most people, but when you’re making a development board and testing nearly every major Arduino library, it’s amazing how handy tools like this can be. So I thought I’d document this little circuit, and especially the 150K feedback resistor trick that makes it work so well with these higher impedances and the chip LMV358 opamp.
Have an amazing project to share? Join the SHOW-AND-TELL every Wednesday night at 7:30pm ET on Google+ Hangouts.
Join us every Wednesday night at 8pm ET for Ask an Engineer!
Learn resistor values with Mho’s Resistance or get the best electronics calculator for engineers “Circuit Playground” – Adafruit’s Apps!
Maker Business — Jenny Lawton COO of TechStars @jennylawton @techstars
Wearables — Cool down
Electronics — Trouble with LM741
Biohacking — EEG Options for Brain Control Interface Projects
Sorry, the comment form is closed at this time.