samig1313
Posts: 1
Joined: Mon Jul 29, 2019 1:43 am

Need help mapping out multiple things to Raspberry Pi

Mon Jul 29, 2019 1:57 am

We are trying to make a snake tank that basically takes care of itself.

We plan to hookup:
- 1x DHT22 (temp/humidity sensor)
- 2x DS18B20 (temp sensors)
- 1x small LCD touchscreen
- 2x 5V fans - one of which is on the case
- 1x led light strip (to simulate a day and night cycle)
- 1x mister/fogger to upkeep the humidity

We have pretty much mapped out how to hook everything up but the issue we are running into is that the Raspberry Pi doesn't have enough power pins. The DHT22 requires a 3.3V hookup, the 2 DS18B20 sensors can one wire to another 3.3V power pin and then the 2 5V fan each use one 5V power pin. So now we have run out of power pins and are confused on what to do as we still have the LCD screen, light strip and mister fogger to hook up.

Any advice would be greatly appreciated.
Thank you.

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neilgl
Posts: 1102
Joined: Sun Jan 26, 2014 8:36 pm
Location: Near Aston Martin factory

Re: Need help mapping out multiple things to Raspberry Pi

Mon Jul 29, 2019 10:03 am

You will need to have separate power supply for the 5V fans , fogged, and LED strip, with gpio pins on the pi controlling their on/ off via transistors or relays (not powering them)

drgeoff
Posts: 9874
Joined: Wed Jan 25, 2012 6:39 pm

Re: Need help mapping out multiple things to Raspberry Pi

Mon Jul 29, 2019 10:35 am

The power pins are electrically capable of multiple connections. There are many ways of overcoming the physical limitations.
Last edited by drgeoff on Mon Jul 29, 2019 12:26 pm, edited 1 time in total.

scotty101
Posts: 3732
Joined: Fri Jun 08, 2012 6:03 pm

Re: Need help mapping out multiple things to Raspberry Pi

Mon Jul 29, 2019 11:18 am

samig1313 wrote:
Mon Jul 29, 2019 1:57 am
We are trying to make a snake tank that basically takes care of itself.
We have pretty much mapped out how to hook everything up but the issue we are running into is that the Raspberry Pi doesn't have enough power pins. The DHT22 requires a 3.3V hookup, the 2 DS18B20 sensors can one wire to another 3.3V power pin and then the 2 5V fan each use one 5V power pin.
You don't need to use a separate power pin for each device, multiple devices can be connected to a single 3.3/5v pin. You just build a breadboard, circuit board or wiring loom to connect the devices to a single pin.
What you do need to consider is how much power will be drawn be each device. Specifically you can't draw a lot from the 3.3v line. I'm sure someone will be able to give you an exact figure but I seem to recall 50mA.

Devices such as the mister, LEDs and fans, would be better served with a separate dedicated power supply.
Electronic and Computer Engineer
Pi Interests: Home Automation, IOT, Python and Tkinter

RGJ-PI
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 23
Joined: Fri May 24, 2019 2:10 pm
Location: Cambridge UK

Re: Need help mapping out multiple things to Raspberry Pi

Wed Jul 31, 2019 7:01 pm

If it were me I'd use a suitably rated (to suit the misters, fans and Pi) external 5V power supply. Power the fans, mister/humidity etc directly from the PSU outputs. Power the Pi directly into the 5V and GND pins on the GPIO header. The DHT22 and DS18B20 sensors you mention will be fine running off the 3V3 pin using the appropriate pullup resistor (to 3V3).

PhatFil
Posts: 1406
Joined: Thu Apr 13, 2017 3:55 pm
Location: Oxford UK

Re: Need help mapping out multiple things to Raspberry Pi

Wed Jul 31, 2019 7:32 pm

Just a thought or 2,,
if using an ultrasonic mister it probably uses an AC psu powered by mains power.
for such a device you may find it a lot easier to use an off the shelf smart wifi power socket to turn on/off as you can mod many of these to respond to wifi/mqtt commands issued directly from your Pi, providing true isolation from the mains :) https://github.com/arendst/Sonoff-Tasmota/wiki
If your Fan and LED lighting is also mains powered i may be expedient also using a smart socket solution for those too.
@ £10-15 per unit it may look more expensive prima-facia but when dealing with mains power the cost of safely boxing diy projects and securing flex with appropriate cable glands and fittings is often overlooked and can be a significant expense proportionally.

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