Multiple dosing pumps with PCA9685

LeonTheLion

New Member
View Badges
Joined
Jan 6, 2022
Messages
8
Reaction score
1
Location
Germany
Rating - 0%
0   0   0
Hey everyone,

since my lighting control is working now i started with the dosing pumps.

Because i‘m an absolute noob the last time i fried my pi zero.
I read about back emf and wondered if there is a protection against it in the circuit from the guide?

Also i‘d like to connect 4 pumps and since i already have the PCA9685 can‘t i use this to generate multiple pwm signals?

Using some transistors to get the right voltage and using the L293D should work, right? If someone could point me into the right direction (e.g. what Transistor to use, how to handle the emf‘s from the motors etc.)

The peristaltic pumps i plan to use are 12V and 250-300mA.

Thanks in advance

 

attiland

2500 Club Member
View Badges
Joined
Jul 22, 2020
Messages
2,594
Reaction score
4,800
Location
United Kingdom
Rating - 0%
0   0   0
PCA9685 has 16 PWM channels so you absolutely can use it. I drive 10 servos on it in my other project (trains)
I can’t answer you other question though.
 

attiland

2500 Club Member
View Badges
Joined
Jul 22, 2020
Messages
2,594
Reaction score
4,800
Location
United Kingdom
Rating - 0%
0   0   0
So i found this guide for arduino: http://www.learningaboutelectronics...p-circuit-with-an-arduino-microcontroller.php

Instead of the arduino pwm output i would use the outputs from the pca9685.

Is there any benefit of using the
L293ds apart from being able to control direction?
You don’t need directions for pumps.

L293D H Bridge Driver
  • 4 drivers
  • 4.5V to 36V supply
  • 600mA Output Current
  • 1.2A peak output
  • DIP 16 pins
It has higher voltage range than PCA9685 and peak iOS higher too. Not sure what your motor requires. I have only done servos with it on Arduino so I hope someone will chip in with greater knowledge than mine.
 
OP
OP
LeonTheLion

LeonTheLion

New Member
View Badges
Joined
Jan 6, 2022
Messages
8
Reaction score
1
Location
Germany
Rating - 0%
0   0   0
@attiland The only specs the peristaltic pumps show are 12V and about 300mA each. Wouldnt that be too much when all 4 pumps are running? Also i want to use only one Pi for everything so pwm capable outputs are scarce.

I tried the setup i mentioned earlier and it kinda worked. I applied a fixed 5V to the transistor base (that would be the max pwm signal from the pca9685 right?) and the motor spinned. But the transistor began immediately to smoke. When I added a 10k resistor to the transistor base the smoking stopped but the motor seemed to spin only occasionally (i use a breadboard and jumpers. Maybe thats the problem)

You see im kinda lost here…

image.jpg
 

Ranjib

7500 Club Member
View Badges
Joined
Apr 16, 2016
Messages
9,825
Reaction score
17,041
Location
Pleasant Hill, Concord
Rating - 0%
0   0   0
You can use dedicated l293d IC for the 12v pumps (1 IC for every 2 pump) or a logic level mosfet that can be driven by pca9685 (example: https://www.adafruit.com/product/355) . Both of these two routes will allow you to draw higher current that you will not be able to do with ULN2800.
Again all this is to support the higher current draw. For l293d you can just use it with fixed direction by shorting the EN pins to 3.3V.
 
OP
OP
LeonTheLion

LeonTheLion

New Member
View Badges
Joined
Jan 6, 2022
Messages
8
Reaction score
1
Location
Germany
Rating - 0%
0   0   0
Ok, thanks. I ordered some IRLB8721 MOSFETs that should arrive tomorrow.

Can you point me to a diagram? I guess i should still use a flyback diode?
 

Mastering the art of locking and unlocking water pathways: What type of valves do you have on your aquarium plumbing?

  • Ball valves.

    Votes: 53 48.6%
  • Gate valves.

    Votes: 60 55.0%
  • Check valves.

    Votes: 25 22.9%
  • None.

    Votes: 28 25.7%
  • Other.

    Votes: 9 8.3%
Back
Top