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What the minimum current input that must be provided to Pi's GPIO input in order to get high value?

The idea: I will be adding Microwave Doppler which output are in micro amperes. I want to know if it will be able to read high input into pin.

Ghanima
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Audrius Gailius
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2 Answers2

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This answer provides some insight in the electrical characteristics. The input current however is something nobody usually cares about as in digital circuits we usually assume low impedance outputs and high impedance inputs. That's fairly save to assume unless one considers "strange" logic families like ECL (a current-steering logic). That however is not relevant to the Pi.

GPIO Electrical Specifications (from Milliways' answer linked above) tries to give some estimates based on similar ARM based chips. Especially the Freescale MCIMX31 multimedia application processor (Table 15) lists a maximum input current for a high impedance input gate without pull-up/pull-down resistors of 1 microamp.

While this is just an estimate of a "similar" chip and the real Pi's SoC might be orders of magnitude different, it at least shows that there might be an issue down that road when connecting that particular source to a GPIO pin. Proper buffering with an additional external high impedance opamp, i.e. see here, seems to be the save way to go.

Ghanima
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From the Official Raspberry Pi Foundation site:

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In terms of minimum voltage I wouldn't go with anything less than 5V.

The maximum GPIO output is around 16mA per individual pin or all pins at ~3mA for a total of around 51mA.

For more details I suggest you give this post and this post a look.

Darth Vader
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  • I don't think this answers the question...and I don't think the maximum GPIO output is anywhere close to 800 mA either. By this I mean the actual pins referred to as "GPIOs", and not the dedicated 3 and 5 V power pins. – goldilocks Jun 01 '17 at 13:27
  • The question despite me trying to find some meaning through editing it is quite ambiguous. I was hoping to give the OP some info on the current draw of the different models of Pi. Especially given they did not specify a model in their question. Having checked my facts again I misquoted the 800mA figure and I'll edit the answer so it contains the correct infomation. – Darth Vader Jun 01 '17 at 13:31
  • I agree with goldilocks. The question is ambiguous (to say the least) but it was user tagged with gpio so I think it's a GPIO question rather than a power-supply question. – joan Jun 01 '17 at 13:31
  • Definitely I was asking what is the minimum current to the gpio input? I edit the question. – Audrius Gailius Jun 02 '17 at 10:02