Power Limit, External Supply?


#1

Hey everyone:

New here. About to buy a GrovePi for a senior design project. But to do what we need, the GrovePi must operate several grove relays, and maybe some sensors. (http://www.seeedstudio.com/wiki/Grove_-_Relay)

Now my questions:

  1. How much power (or how many amps at 5V DC) can the GrovePi send to peripherals overall without frying the pi or the GrovePi’s components?
    The GrovePi receives most of its power from the 2,4, and 6 pins on the pi I’m guessing?

  2. Can I give the GrovePi external power, and send more current?

  3. Are there any other limitations on what kinds of Grove Sensor’s I can use? I saw that only 3 analog sensors can be used, is that correct?

Trying to do my own research here, but I’m finding dumb-ed down information hard to come by… I want to learn! Just need help starting.
Thanks for any responses! -Aaron


#2

Hey,
The GrovePi should be able to operate a lots of relays, as many as 11 of them.

Here are the answers to your questions:

  1. The limitation to the current is the amount of current the Pi can supply on the 5V pin. The Pi can supply 1.2A max and if you remove the power taken by the Pi any USB peripherals, you’can have somewhere between 200-500mA left. It would be better not to take more than 300mA though.

  2. No, you cannot give external power to the GrovePi as such. If you have a device which takes a lot of current, you can disconnect the red wire from the grove connector and power it from an external supply with a shared ground. GrovePi would control the I/O’s and the external supply would be used to power it.

  3. There is no limitation as such but do check which sensors have examples in the Github page: https://github.com/DexterInd/GrovePi/tree/master/Software/Python . We don;t have examples for some of the sensors but it should be easy enough to write them. You can only use 3 Analog sensors on the GrovePi, but you can stack multiple GrovePi’s to get more ports or use Grove ADC;s http://www.seeedstudio.com/depot/Grove-I2C-ADC-p-1580.html to get better precision and more ADC ports.

Do let us know if you need any more help.

-Karan


#3

Hey…

Thanks for answering. So, understanding that you were just giving me an estimation:

Bad news:
If we use anything more than about 3 relays (which claim an operating current of 100mA), we will have to start giving each sensor or relay external power individually.
(And I would hook the shared ground up to each individually, or just a ground connection somewhere on the grove/pi?)

Good news:
We can plug in grove ADC’s to digital ports and use them to read analog signals. Which gives us up to 15 analog readings with one GrovePi, neglecting the power supply issue.

Appreciate your time,
-A


#4

Hey,
Yeah, it looks like GrovePi would only be able to handle a few of the Grove Relay’s because of the 100mA operating current for each. Just a single shared ground b/w the GrovePi and the external power supply would be enough and for each of the relays, do connect all the three lines except the +5V which would be externally powered.

-Karan