I recently bought a set of Digispark “blue” boards from Aliexpress with the USBC connector.
I upgraded the firmware to 2.6 and loaded my code, which just takes a trigger signal in on PB0 and drives three of the inputs on a ULN2003 board from PB2, 3 and 4.
Wired it up and it all worked as expected. Happy days.
Then a couple of power ups later, the board is dead. One output is stuck high and it’s no longer recognised by the firmware batch file or the IDE. I just get the Windows device not recognised error when it’s plugged in.
Tried it with another of the boards with the same result. Worked for a few minutes then expired.
So I loaded one of the older boards I have, put a 500R resistor in the input line and 1K in the outputs to the ULN and it’s been working ever since.
The input is from a 5V digital output (20cm away) and the inputs are going straight to the ULN (1cm away), so surprised they need resistors to protect them.
I’m going to be making quite a few of these boards, so want them to be reliable.
As an aside, I’m using the DS because it comes with mounting holes. How do people integrate something like the Pro Mini into a cased project ? Heatshrink and hot glue :-O ?
Yes, that’s the one. With the larger USBC socket, they have moved everything closer to the lower edge of the board, so the AT85 actually sits over where the silkscreen markings should be for P3-P5
This is simply the series prefix used by the original manufacturer (Sprague / Allegro) for this family of devices. There are many different devices in several configurations. They also make devices that are similar but have different input formats.
Hint: The ULN2003 and ULN2803 families both turn on at low logic voltages (around 2 to 3 V), but the ULN2003 is generally better suited for lower-voltage drive because its input resistors are optimized for 5 V TTL logic. For 3.3 V logic, neither is ideal, but they usually still work.
Post an annotated schematic showing what you used and how it was connected.
At this point, with the limited information available and based on my past experience with Digispark, the parts may not be properly applied. Digispark did not manufacture the parts; they produced modules that utilize the parts, making them easier to use.
It may be something to consider to just have PCBs that you design manufactured and add components such as ULN2003 directly soldered on the board and ATtiny85 or ATmega328P socketed on the board, add supporting components like capacitors and resistors, instead of trying to use things like DIgispark or Pro Mini boards and ULN2003 boards. That would probably be my approach for “making quite a few of these boards.”
