EEVblog > EEVblog Specific

EEVblog 1491 - The MacGyver Project - Part 1

(1/5) > >>

EEVblog:
Part 1 reverse engineering the interface on the LED display of the Banshee Ultrasonic gas leak detector to make a MacGyver type countdown timer THING (for demonetisation purposes).
This will be a choose your own adventure project, I don't have anything planned, so let me know what you want to see!

Per Hansson:
I think seeing this multiplexed and running on a Raspberry Pi Pico (ARM RP2040 MCU) would be the most interesting, it can also then possibly make use of the infrared sensors to be able to set the countdown time "remotely" :)

DiodeGoneWild did a video on a ring tester where he shows multiplexing via a Attiny24 that some might find interesting:
https://youtu.be/QBbEYYWiBI8?t=523

Kleinstein:
The LED on the Q7 output limits the signal voltage available to drive the next stage.  So one may have to use blanking, not just for the visual, but just to make it shift to the 2nd chip.

The on resistance of the 74HC chips goes up with less supply voltage. With low enough a supply (likely somewhere in the 2.5-3 V range) the LED current should be at a reasonable level (like 5 mA) so that the chip can atually drive it. To still get a valid logic level for the next stage, something like a diode in the common cathode line may be a good idea.
So the easiest way is likely a reduced supply voltage.


Driving external shift registers is a bit odd with discrete logic. So the logic choice for the control would some kind of µC. Which one to a large part which ones are actually available. Many of the modern ones are ok with some 2.5 - 3 V.

Ivan7enych:
Crazy idea - count a number of segments in a microcontroller, multiply it by required current per led (3-6mA), and set it into DAC driven current source. :)

Second idea - to use a tuned fixed voltage on a common cathode, and use internal output resistance of 74HC chips as a simple current regulation for each led. But there will be a large thermal dependence...

Fungus:

--- Quote from: Per Hansson on August 05, 2022, 01:30:45 pm ---I think seeing this multiplexed and running on a Raspberry Pi Pico (ARM RP2040 MCU) would be the most interesting, it can also then possibly make use of the infrared sensors to be able to set the countdown time "remotely" :)

--- End quote ---

It'll be an awful lot easier to do on an Arduino where the pins can drive LEDs directly.

Navigation

[0] Message Index

[#] Next page