Is there a way to control motor speed without any chips

[baronobeefdip]

I am on a budget and all of the tutorials on motor speed control with a raspberry pi have been involving chips in order to do so. I am on a budget and have no time or money to go out and hunt down chips. Even though some might be relatively easy to find, and cheap, I don't want to spend money on them. I am wondering if there is a way to control the speed of a motor by simple use of a GPIO pin and transistor.

[RST8]

I am on a budget and all of the tutorials on motor speed control with a raspberry pi have been involving chips in order to do so. I am on a budget and have no time or money to go out and hunt down chips. Even though some might be relatively easy to find, and cheap, I don't want to spend money on them. I am wondering if there is a way to control the speed of a motor by simple use of a GPIO pin and transistor.

Short answer is No.

GPIO can provide tens of milliamps. A motor needs significantly more. You risk damaging your Pi, which is going to cost you a lot more than getting a suitable chip or power transistor.

[rpdom]

I am on a budget and all of the tutorials on motor speed control with a raspberry pi have been involving chips in order to do so. I am on a budget and have no time or money to go out and hunt down chips. Even though some might be relatively easy to find, and cheap, I don't want to spend money on them. I am wondering if there is a way to control the speed of a motor by simple use of a GPIO pin and transistor.

Short answer is No.

GPIO can provide tens of milliamps. A motor needs significantly more. You risk damaging your Pi, which is going to cost you a lot more than getting a suitable chip or power transistor.

The OP mentions a transistor...

[joan]

Yes, you have to implement the functionality of the motor driver in discrete components. That might be feasible if you already have all the needed diodes, resistors, and transistors, otherwise it may be cheaper to order a inexpensive motor driver board.

E.g. http://www.ebay.co.uk/itm/351527222931 will drive 2 DC motors forward and reverse and accept PWM speed control.

[mikronauts]

Save yourself a lot of headaches, and use an L293D chip.

I am on a budget and all of the tutorials on motor speed control with a raspberry pi have been involving chips in order to do so. I am on a budget and have no time or money to go out and hunt down chips. Even though some might be relatively easy to find, and cheap, I don't want to spend money on them. I am wondering if there is a way to control the speed of a motor by simple use of a GPIO pin and transistor.

[baronobeefdip]

Save yourself a lot of headaches, and use an L293D chip.

I am on a budget and all of the tutorials on motor speed control with a raspberry pi have been involving chips in order to do so. I am on a budget and have no time or money to go out and hunt down chips. Even though some might be relatively easy to find, and cheap, I don't want to spend money on them. I am wondering if there is a way to control the speed of a motor by simple use of a GPIO pin and transistor.

Yeah based on the other responses that seems to be the way to go, but I have heard of just simply using an assortment of transistors and I might check that out to make things more clearer. In the meantime, ordering that chip would have to come all the way from China and a deliver like that could take about a month which is time that I don't have.

[DougieLawson]

Save yourself a lot of headaches, and use an L293D chip.

+1
For £3 / $3 it would be a false economy not to use one.

[baronobeefdip]

Save yourself a lot of headaches, and use an L293D chip.

+1
For £3 / $3 it would be a false economy not to use one.

From what I have been seeing, the big caveat for me would be that I would have to wait a month for it to get to me.

[DougieLawson]

From what I have been seeing, the big caveat for me would be that I would have to wait a month for it to get to me.

That's better than having to wait a month for a new $35 RPi.

If you want to build a H bridge with discrete components watch this video https://www.youtube.com/watch?v=SsB_ezlict4

[baronobeefdip]

From what I have been seeing, the big caveat for me would be that I would have to wait a month for it to get to me.

That's better than having to wait a month for a new $35 RPi.

If you want to build a H bridge with discrete components watch this video https://www.youtube.com/watch?v=SsB_ezlict4

I guess I have a bit of a poor man's arrangement but I am not sure how it will all go. the schematic in the following link is the best that I can do.

http://i.imgur.com/a8GwOoh.jpg

All the gpio lead on the left side of the schematic will not all be turned on at the same time. Each lead will be activated alone while the others have no current flow. meaning that whenever a gpio port is on, it will go through a different number of resistors along the way. the lead at the very top is the connection which goes through no resistors so it powers the motor at full power, while the ones below it will go through either one or more resistor depending on which one is activated. these varying degrees of resistance will alter the current and then run the motor at different speeds depending on the resistance applied to the base of the transistor. I am hoping that this might be an appropriate connection.

[boyoh]

I don't think your Idea will work, using a ladder network of resistors and witching it with out/puts.

A out/put will be ether 1 ( high ) or 0 ( low ) Your resistors will not be additive ( Shorted out)

[danjperron]

Before buying any motor driver, we should know what kind of motor you want to connect to the Pi. This is a big consideration and it is the first one.


Is it a AC, DC , Servo or a stepper?

It is a 2 H.P. or a little toy motor?

What is the Voltage, running and stall current?

What will be the purpose of the motor?

[mikronauts]

+1

Before buying any motor driver, we should know what kind of motor you want to connect to the Pi. This is a big consideration and it is the first one.


Is it a AC, DC , Servo or a stepper?

It is a 2 H.P. or a little toy motor?

What is the Voltage, running and stall current?

What will be the purpose of the motor?

[mahjongg]

I guess I have a bit of a poor man's arrangement but I am not sure how it will all go. the schematic in the following link is the best that I can do.

http://i.imgur.com/a8GwOoh.jpg

All the gpio lead on the left side of the schematic will not all be turned on at the same time. Each lead will be activated alone while the others have no current flow. meaning that whenever a gpio port is on, it will go through a different number of resistors along the way. the lead at the very top is the connection which goes through no resistors so it powers the motor at full power, while the ones below it will go through either one or more resistor depending on which one is activated. these varying degrees of resistance will alter the current and then run the motor at different speeds depending on the resistance applied to the base of the transistor. I am hoping that this might be an appropriate connection.

That won't work, if only for the simple reason that connecting a GPIO to the base of a NPN transistor (which has its emitter tied to GND) is big no-no, you are in essence tying a diode between the GPIO and GND, and that will draw unlimited current from the GPIO when it is trying to put 3.3V on the anode of this diode, this will destroy the GPIO, and with it the SoC (broadcom chip).

If the big idea is to have a variable current flowing into the base of the transistor (which is somewhat of a valid idea), then your network is laid out wrong, you should tie all resistors on one end (the end connected to the transistors base) together, and use resistors with a binary sequence of values, say 1K, 2K, 4K, 8K each controlled by a GPIO pin, that at least would give you a chance of adding currents together (at least if you also put a diode in series with each resistor, so that a GPIO can only source a current, not sink it too). then you can adjust the flow through the base of the transistor, but that isn't enough. but its a beginning, and also you MUST add a diode over the motor, or stopping the motor will induce large negative voltages over the motor, which may blow the transistor and the GPIO's.

[ame]

You could modify a servo for continuous rotation. Then you get speed and direction control from one GPIO, and no chips.

[BMS Doug]

You could modify a servo for continuous rotation. Then you get speed and direction control from one GPIO, and no chips.

You can also buy them pre-configured for continuous rotation.