I've ordered some MAX485 chips to establish a connection between a RPi and multiple Arduino Mini's. This is working great, but the MAX485 chip on the RPi side gets quite hot. I've burned around 4 chips until now. I don't know what I'm doing wrong, as it seems to send and receive contents correctly.

Below is a picture of the MAX485 sending and receiving data with Python: PuTTY showing the MAX485 chip working

I've hooked it up this way:

Wiring MAX485

In operation it gets around 40-45°C.

I've tested letting the transmit Pin "High", and then it gets really hot (to the touch, far more than 45°C). After a few days, it simply doesn't work anymore. No visible sign of damage, but it receives/sends unreadable garbage.

Any help is greatly appreciated.


EDIT: Here a picture of what a "broken" chip does: (This chip isn't that much damaged, I've burned others that I won't even recognize a single character) Broken chip receives garbage

EDIT 2: When the Transmit Pin is "LOW" (0.01V): 28.4°C when the Pin is LOW

And when the Pin is "HIGH" (3.26V), after just 5 minutes (and raising): 42.1°C when the Pin is HIGH

EDIT 3: For the sake of completeness, I checked the datasheet and the voltages that I'm driving to the MAX485 Transmit Pin, are totally acceptable: MAX485 Voltages

And the 5VDC that I'm driving the MAX485 is also acceptable:


EDIT 4: I have tested putting an 1K resistor between the Transmit Pin (RPi -> MAX485), but no success, it continues raising the temperature. When I tried a 2K, the MAX485 didn't even pull the transmit "flag", in other words, nothing was sent through (and it still got hot very quickly).

  • Your module appears to be running at a 5V logic level. Do you have anything between the module and the Pi to convert between 5V and the 3.3V required by the Pi's GPIO pins? – goobering Apr 20 '17 at 12:47
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    That's likely to be a problem. The Pi's pins are only 3.3V tolerant. If you feed a 5V signal into one of them you're likely to do some damage to the Pi. I don't know for sure what happens in the other direction, but your module is likely to be happier if you feed it the 5V it's expecting rather than the 3.3V supplied from the Pi's pins. You could try using a logic level converter or voltage divider between the Pi and the module to convert appropriately. – goobering Apr 20 '17 at 12:54
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    40-45°C isn't enough to burn an IC out, in fact the datasheet says it is fine to 70°C. If there were enough heat to damage it, it should be at least very uncomfortable to touch for more than a few seconds. However, incorrect TTL levels will produce errors; the problem isn't just the high, it's also the low threshold. – goldilocks Apr 20 '17 at 13:14
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    Anyway, if you are dead set on pursuing that, I suggest you take it to our larger sibling site, Electrical Engineering. There isn't anything here that is particularly pi specific (besides the fact you have it connected wrong). – goldilocks Apr 20 '17 at 14:40
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    @Fusseldieb Not here. This is not a MAX__ IC site. If the folks at E.E. think you have a point, great, in which case it belongs there. But IMO you have become very confused. – goldilocks Apr 20 '17 at 16:54

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