What do I need?
I am told that I need some transitors. I have a 12v powerpack and 2 x12v motors. How do I set this up so that I don't blow-up the RPi and that I can control the motors through the GPIO?
I have a gertboard on the way but I would like to see if I can do it without it first.
I have little knowlegde about transitors and electronics but I do know how to build circuits.
Sorry, I have been out of town most of the week.
I have an update to the schematic to correct errors caught by Michael Kellet.
He made me think about small amount of current heeded by the L239D chip.
Another way to think of it is a high impeadance input. So we don't need
a lot of current gain in the transistor.
While darlingtons are high current gain.
The current on the chip input/transistor output will be set low by the high chip input impeadance.
When you use a transistor as a switch, you set the Ib * Hfe to be larger than where the ciruit
will operate in order for the transistor to alternate between cut off and saturation.
So I upped the resistor values but did not set Ib * Hfe to match the current needed by the
chip but rather to provide 10 or more times as much.
The real current will by limited by the chip input impeadance and you have a low voltage
dropped across R4/R5/R6.
Ib is the transistor base current.
Hfe is the transistor current gain.
By lowering the base current, we ask the Raspberry Pi to provide less current.
I drove motors with an Arduino. It runs on 5 Volts. It has analog inputs. It has lots of PWM
outputs. It won't run Linux or Python.
I have not yet tried the one PWM output on the Pi. I don't know if a PWM driver is ready or not.
An 8 but micro-controller normally has PWN hardware outputs.
Software pwm is where you turn the GPIO output off and on and increase the speed
by having it on a higher percentage of the time.
I've thought of connecting an Arduino to the PI with 5 Volt serial or I2C and having the
Arduino do motor control but probably not get to it.
I have driven stepper motors directly of a GPIO with Darlingtons but without an H bridge chip.
Any way here is the updated schenmatic in PNG. I am trying to attach the Eagle schematic.
 |
Sorry, I have been out of town most of the week.
I have an update to the schematic to correct errors caught by Michael Kellet.
He made me think about small amount of current heeded by the L239D chip.
Another way to think of it is a high impeadance input. So we don't need
a lot of current gain in the transistor.
While darlingtons are high current gain.
The current on the chip input/transistor output will be set low by the high chip input impeadance.
When you use a transistor as a switch, you set the Ib * Hfe to be larger than where the ciruit
will operate in order for the transistor to alternate between cut off and saturation.
So I upped the resistor values but did not set Ib * Hfe to match the current needed by the
chip but rather to provide 10 or more times as much.
The real current will by limited by the chip input impeadance and you have a low voltage
dropped across R4/R5/R6.
Ib is the transistor base current.
Hfe is the transistor current gain.
By lowering the base current, we ask the Raspberry Pi to provide less current.
I drove motors with an Arduino. It runs on 5 Volts. It has analog inputs. It has lots of PWM
outputs. It won't run Linux or Python.
I have not yet tried the one PWM output on the Pi. I don't know if a PWM driver is ready or not.
An 8 but micro-controller normally has PWN hardware outputs.
Software pwm is where you turn the GPIO output off and on and increase the speed
by having it on a higher percentage of the time.
I've thought of connecting an Arduino to the PI with 5 Volt serial or I2C and having the
Arduino do motor control but probably not get to it.
I have driven stepper motors directly of a GPIO with Darlingtons but without an H bridge chip.
Any way here is the updated schenmatic in PNG. I am trying to attach the Eagle schematic.
|
How would I subsitute in a Darlington Pair into your schematic? I have a ULN2003 Darlington IC transistor array. See the datasheet below: http://www.jaycar.com.au/products_uploaded/ZK8855.pdf
Also, If I want to run two motors through PWM, then I would have to 'piggy back' off the circiut that is already present. See My Schematic (experimental) based off yours below. I think this becasue the raspberry Pi (as far as I know) only supports 1 'connection' of PWM. Am I correct?
One other thing, is the 5 volts coming out of the Raspberry Pi or an externatal source?
I know that. 
It was to much time to add to the diagram.
