Hello I want to use an 1.5V DC motor with the ARDUINO Uno without a motor shield. How can I transform the value from an output pin down to 1.5 V? The PWM isn't working in this case.
The Arduino output pins will most likely be destroyed if you try to use them to power a motor.
You must use a transistor or a motor shield to run a motor, and usually, a separate motor power source to avoid noise problems with the Arduino. Connect the grounds of the Arduino and the motor power supply together. If you search through the forum, there are plenty of examples.
Use a transistor and the PWM will work.
This is a simple task.
http://www.bit-101.com/blog/?p=3831
I guess a relay is "unthinkable"?
No voltages to "drop", just switch (literally) a battery on/off. Simple
Hello I want to use an 1.5V DC motor with the ARDUINO Uno without a motor shield. How can I transform the value from an output pin down to 1.5 V? The PWM isn't working in this case
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I guess a relay is "unthinkable"?
I wouldn't have thought of it but I'm glad you brought it up because it made me realize I didn't answer the OP's question about how to drop the voltage from 5V to 1.5V.
@OP,
It's called a dropping resistor , and the formula is:
Let ILoad = 150mA =0.150A
Then,
RDROPPING = (VIN-VLOAD)/ILOAD
RDROP = (5-1.5)/0.150A = 23.33 ohms = 22 ohms
PLoad = ILoad * VLoad = 0.150A * 1.5V = 0.225W = 225mW = 1/4W
You should measure the current to verify it is approximately correct. If it is higher, recalculate for the higher value.
You should be ok with a 1/2W resistor but worst case a 1W resistor.
Put a 22 ohm , 1/2 W resistor between the + Motor lead and the 5V dc supply pin , and replace the 9V battery in the linked tutorial with the 5V supply from the arduino. If the motor is truly a small motor it should be ok running from the onboard regulator, if you connect the 9V battery to the arduino external dc input barrel jack. If however, you try to run it off the USB
power , which can only supply 500mA, it may pull down the arduino 5V causing it to reset. If that happens you know you need to use a 9V battery connected to the arduino barrel jack but the motor connected to the 5V pin with the 22 ohm resistor in series.
Motor current isn't constant, it varies with the work it does (stall current vs spinning away unloaded.)
How does that dropping resistor idea work out then?
[Think diodes, not so great - or a pass transistor, better.]
dwg attached, motor gets 1.5V, PWM-able; let the OP post
I didn't answer the OP's question about how to drop the voltage from 5V to 1.5V.
.... but he most likely only asked that question because of the misconception about driving it from the Arduino 5V in the first place.
If you choose the right PWM duty cycle then you don't need to drop the voltage the motor will work quite happly off pulsed 5V.
Motor current isn't constant, it varies with the work it does (stall current vs spinning away unloaded.)
How does that dropping resistor idea work out then?
This is a valid point. I think Mike's comment addresses this issue and seems to imply that a constant current transistor circuit is not needed for the transistor driver. I am opposed to the relay approach because it has drawbacks, like contact arcing and no speed control . Adding a constant current feature to the transistor driver is do-able but I think Mike's comment indicates it is not necessary.
In answer to your question, the resistor will dissipate more or less heat as the motor current varies and the voltage will vary accordingly, so it doesn't work out that good but that is not the same as saying it won't work at all. Using a relay doesn't provide speed control. If you add a 1 ohm resistor between the emitter and ground, you can use that to measure the current with an analog input on the emitter and use that feedback info to control the analogWrite value. You probably know more about how to do that than I do but I know it is doable. If might take me a few hours to get the code dialed in and it might take you a few minutes but both of us would get it done and it would work just fine, without the relay. I don't think we need to get into the low pass filter with appropriate size cap to filter the varying voltage before measuring it with the analog input. I think you can concede that if low pas filter values are correct, the voltage at the analog input will vary as a function of the RC time constant of the low pass filter. Whether or not that response time is fast enough is another question (maybe for another day)
that is probably not relevant in this application.
raschemmel:
Motor current isn't constant, it varies with the work it does (stall current vs spinning away unloaded.)
How does that dropping resistor idea work out then?This is a valid point. I think Mike's comment addresses this issue and seems to imply that a constant current transistor circuit is not needed for the transistor driver. I am opposed to the relay approach because it has drawbacks, like contact arcing and no speed control . Adding a constant current feature to the transistor driver is do-able but I think Mike's comment indicates it is not necessary.
I don't think anyone has proposed a "constant current feature". I know that I haven't.
I showed a voltage regulator. The voltage available to the motor is VB - VBE
2.5V - 1V = 1.5V
raschemmel:
Using a relay doesn't provide speed control.
I still don't know if that's required. The OP has made one post.
We could go on all day anticipating this and that (not at all unusual around here.)
I showed a voltage regulator. The voltage available to the motor is VB - VBE
2.5V - 1V = 1.5V
In all fairness I think your suggestion is a better choice than the circuit I linked with a dropping resistor added. I concede that without argument.
[EDIT: 7:37 am PST 7/8/2014]
We could go on all day anticipating this and that (not at all unusual around here.)
I think it would be safe to say that every forum post is different and takes on a life of it's own , based on the question and the OP.
Often one of these two factors will put a spin on the post and it will go in a direction it might not have normally (if there is such a concept here) . An OP that is 11 years old can definitely be enough to alter the 'course' for obvious reasons. Some people want to hold there hand and talk in a soft cuddly voice, and others (like myself) will come right out and say "If you want to be treated like an adult, you came to the right place. If you want to be treated like a child, post somewhere else.". It would not be a stretch to say that posting on the forum is a little like throwing a small piece of red meat to a pack of hungry dogs and watching them fight over it. One might also say that posting on the forum can be likened to being stoned to death in the town square with ideas of various sizes and shapes. Sometimes a really nasty OP with a stupid question and an arrogant demanding attitude can bring people out of the woodwork. Conversely a really nice (or young ) OP can attract helpful people who want to contribute. You just never know what to expect.