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Old 29th Nov 2022, 10:05 pm   #39
Slothie
Octode
 
Join Date: Apr 2018
Location: Newbury, Berkshire, UK.
Posts: 1,287
Default Re: Tesla Programmer

Quote:
Originally Posted by SiriusHardware View Post
Hmm, it's unfortunate that this situation (with low grade clones) has arisen but it means that your / our / anyone's circuit should anticipate an end user almost certainly trying to use one of those clones at some point and dodge that bullet by not trying to back power the Arduino.

If you do it will only lead to people complaining that 'your project blew my Arduino up'. You saying that it happened because their Arduino wasn't a real one won't carry any weight because it will have worked perfectly in every other Arduino application they used it in prior to that. You can see where I'm coming from.

Therefore, if there is a solution which will work equally well for both real and clone Arduinos, we should really try to do it that way.
In which case, I'd give them a full refund of the money they paid me to design it....

But seriously, I agree in principle, it is far from optimal to produce a design that has a flaw like this, no matter how carefully you document the shortcoming or put big flashing warning signs on the box. That said it didn't happen to the first UNO I used (with a DIP chip) and I didn't notice with the SMD Chinese clones until I tried using it in another project, as it was only the regulator that stopped regulating, it still worked from USB power!

If you don't back-power the arduino, it gets powered through the pull-up resistors on the inputs and excess current flows through the ATMEGA (I measured 200ma rather than the usual 16mA and it got quite warm). You have to pull up the inputs so that you know when the pins have been pulled down. There are 2 ways to fix this: put the ATMEGA on the sheild and produce what is essentially a stand-alone design powered from the 12v supply. This I wanted to avoid given that most people would use it 2-3 times, then put it in the old projects box. Or you could detect the 5v rail on the Arduino and use that to switch the 12v supply which is possible but I'd have a hard time squeezing the extra MOSFET onto the sheild as there is hardly room for a resistor at the moment. Perhaps a future redesign using SMD components could acheive this, but I wonder how much demand there would be to warrant making this change - if it ends up I need to redo the board to get a working programmer then I will probably consider this (there are currently 2 changes I've had to bodge in so this isn't entirely unlikely). My current focus is getting something to work when used with care so I can produce a PROM once in a blue moon.
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