Timeline for Attiny85 crashes when I run a motor through an L293D
Current License: CC BY-SA 4.0
15 events
| when toggle format | what | by | license | comment | |
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| Apr 9, 2019 at 21:25 | comment | added | DKNguyen | As I just mentioned larger capacitors don't work at higher frequencies where the effect of parasitic inductances are most prominent. This inductance is why you have to place the smaller capacitors close to the chips. In other words, with larger capacitors, you don't need to worry about as much with physical placement and closeness. So just one 1000uF for everything should be enough. | |
| Apr 9, 2019 at 21:19 | comment | added | user2145184 | @Toor Ok yeah that's what I did in the first example, I see the I put the wrong value on it though. Should have been 1000uF. But I'm guessing I need both across the rails and one specifically for the microcontroller. | |
| Apr 9, 2019 at 18:54 | comment | added | DKNguyen | The 1000uF is another decoupling capacitor except it is for your motor. So it goes straight across your power rails. Larger capacitors are for lower frequencies where distance does not matter as much so it doesn't have to be as close as possible to your motor. What @ChrisStratton is talking about is how motors pull a current at least several times higher than the maximum current on startup since they are basically stalled on startup. This is too short and fast to see with a multimeter. You need a scope to see it. | |
| Apr 9, 2019 at 15:32 | comment | added | user2145184 | I don't have any extremely precise equipment, but checking max current with a multimeter says 0.25A, and my power supply is rated for 3A. | |
| Apr 9, 2019 at 15:27 | comment | added | user2145184 | @ChrisStratton Where do I put the 1000uF capacitor? When I tested, I put it across V and GND of the power supply where it entered the circuit. | |
| Apr 8, 2019 at 21:25 | comment | added | DKNguyen | Motor load changes are really up to the application so it's an unknown right now so it's premature to say it's undersized. If anything the driver is undersized for what the supply can provide but that capacity might not be needed for the application. And any stalled motor is going to drag down a supply of any reasonable size so that's a moot example. | |
| Apr 8, 2019 at 21:23 | comment | added | Chris Stratton | What happens when the load on the motor changes? When whatever it spins gets mechanically stuck? | |
| Apr 8, 2019 at 21:22 | comment | added | DKNguyen | Hah, right you are. That cap should be going across the power rails. A decoupling cap just for the motor, so to speak. I do question the reasoning that the supply is undersized if adding a capacitor satisfies the surge requirements. It can't be expected to be able to straight up supply the surge current all the time. | |
| Apr 8, 2019 at 21:16 | comment | added | Chris Stratton | Read their actual statement and you'll see that they put that cap in an utterly useless place. | |
| Apr 8, 2019 at 21:15 | comment | added | DKNguyen | OP has stated that they already added 1000uF caps prior to adding this post which should have alleviated current surge issues from the motor. | |
| Apr 8, 2019 at 21:14 | comment | added | Chris Stratton | Motors draw much more than steady state when starting. Again, bypass capacitors are a good idea. But they are not a sound solution to this problem. | |
| Apr 8, 2019 at 21:11 | comment | added | Chris Stratton | No. While that is a good idea as a general principle, it is not the issue here. The issue is that the motor is overloading the power supply, whatever that is. If this "solves" the problem it's luck, not sound engineering. | |
| Apr 8, 2019 at 21:09 | vote | accept | user2145184 | ||
| Apr 8, 2019 at 20:55 | history | edited | DKNguyen | CC BY-SA 4.0 |
deleted 46 characters in body
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| Apr 8, 2019 at 20:44 | history | answered | DKNguyen | CC BY-SA 4.0 |