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12volts into Quickstart — Parallax Forums

12volts into Quickstart

prof_brainoprof_braino Posts: 4,313
in Propeller 1
I was testing a 12 volt electronic speed controller (ESC) for a brushless DC motor (BLDC). It works just the same as a regular hobby servo, 1ms pulse every 20 ms is completely stopped and 2ms pulse every 20 ms is max speed, as we would expect.

When the driver was working, I burned the code to EEPROM and disconnected from the PC, and tried to test standalone.

I inadvertently connected the quickstart Vin to 12 volts instead of the 5 volt battery eliminator circuit (BEC). I tested for a bit (it worked as expected) before I discovered the incorrect connection.

Everything still seems to work ok.

I had a 10K thermistor between pin 27 and Vdd with a small capacitor between pin 27 and GND (from another project). When I noticed Vin was connected to 12 volts, I checked the quickstart for damage. I noticed that the capacitor pin is no longer soldered to the ground connection. Could this joint have melted from 12 volts? If the wire was simply broken from previous handling, would 12volts through the thermistor to pin 27 damaged the input, or would the 10k thermistor kept the current at 1mA?

Thanks

Comments

  • FireNWaterFireNWater Posts: 93
    .
    Pshaw. . . no smoke, no harm, no foul . .
    .
  • kwinnkwinn Posts: 8,697
    (12V - 3.3V) / 10K = 0.87mA, which may or may not have damaged the protection diode, but if the pin works as an input and output why worry about it.
  • evanhevanh Posts: 15,918
    Yeah, the thermistor would have kept the current below 1mA - keeping the smoke within P27. The capacitor would have been already like that. I note the AP1117 is rated for up to 18 volts. That's good to know. Shift the thermistor to the 3.3V supply and you can carry on using 12 volts for Vin.
  • prof_brainoprof_braino Posts: 4,313
    Thanks guys!
  • kwinnkwinn Posts: 8,697
    evanh wrote: »
    Yeah, the thermistor would have kept the current below 1mA - keeping the smoke within P27. The capacitor would have been already like that. I note the AP1117 is rated for up to 18 volts. That's good to know. Shift the thermistor to the 3.3V supply and you can carry on using 12 volts for Vin.

    Connecting the thermistor to 3.3V simplifies the circuit and reduces the current draw. It also reduces the self heating effect of the thermistor, although 17.28mW would not affect the reading by much.
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