# How to increase analog output pin current?

Hi

I want to gradually increase voltage and current using analogWrite method of any output pin.
Ranging from 0 to 255, I can see voltage if increasing but current is 40ma. But my requirement is to get more current around 100 or 200ma while increasing voltage to 3.3v.

Any suggestion?

You'll need a buffer since an arduino pin should never be allowed to provide more than 20mA.

Also, an arduino has no analog outputs. What are you trying to accomplish and can you provide a schematic of what you have so far?

First off read how PWM works.
http://www.thebox.myzen.co.uk/Tutorial/PWM.html

You will see it is only the the ratio of on to off time that averages out to make it appear the voltage is changing.

If you want more current capability then you need to use a transistor.

But what are you really doing this for? I hope it is not to drive an LED.

Thanks for your quick reply, I am new to electronics and have less knowledge but i have to control a coil which generates magnetic fields gradually using analogWrite from 0 to 255.

But while using arduino, magnetic fields are not enough but if i use 3v batteries without using arduino my coil generates enough magnetic fields.

I am powering arduino using a 5v 3amp dc adapter.

How about simply driving a low-side mosfet switch from a PWM with the coil between the mosfet and +5V or +3V? In case of 3V you'll need a DC-DC converter or a linear regulator to bring 5V down to 3V.
Since it's a simple coil the voltage probably doesn't matter; you can compensate for a different voltage by adjusting the PWM duty cycle on the driving pin.

Something like this:

Which immediately brings the question: how are you going to limit the current through L1? The green plot is the current through L1 with peaks topping out at 1.4A with this choice of components. Can your coil handle this? Is your software going to be fool-proof enough to not let the pin remain high for long enough to burn out the coil and/or the mosfet used?

You assume OP uses PWM, but it could be DAC enabled board for what we know

This would be a good starting point

As you can see from the above response we need to know about your hardware - specifically in this case which arduino board you are using, and details about the coil.

No assumption he said:-

That is not using a D/A is it?

Why not?

** In addition to PWM capabilities on the pins noted above, the Due has true analog output when using `analogWrite()` on pins `DAC0` and `DAC1` .

Main objective is to create a clock from volt meter. But due to unavailability of 3v or 5v analog voltmeter in the market, i have to create one.

I am using Arduino UNO, and i made a custom coil of 150 turns of copper wire of 40 gauge to create a 3 to 5v DC analog volt meter with a small magnet. I can see my custom voltmeter works perfectly with external power sources but with arduino, it moves pointer but not good enough. i think due to low current from output pin.
However, i am going to check pwm also for more knowledge.

If with arduino or with any other hardware, somehow able to supply 100 to 400ma current with 3.3v then i think I can proceed.

I am increasing voltage from 0 to 3.3v using analogWrite method of my program. So at 0 my custom voltmeter pointer remains a 0 but at 3.3v the pointer is not moving to highest due to low current. However, when i use 3v batteries it works perfectly. I am sorry, providing such abstract information as per my best knowledge of electronics.

Yes and post #5 from @koraks showed you how to do this, with L1 being your electro magnet. I would just move R2 to the other side of R1.

Forget about the 3V3, that will be taken care of when you calibrate the duty cycle you need to point to the right number.

Yeah, that's better. It'll work the way I drew it but moving R2 gives a bit more leeway in mosfet selection.

use any analog meter, open it you will see the wires from coil connect 50k resistor in series with coil, apply 5V and look how much the pointer is moved, than adjust the resistor value.

@79galinakorczak this is good advice. For starters, it prevents the somewhat doubtful situation of needing several hundred milliamps to drive a simple needle gauge. That might have been acceptable in 1830, but it's kind of awkward today.

some analog meters require only 50 micro amps, so 20 mA ......

so you don't need a buffer.

@79galinakorczak I have doubt with AC analog meter which I have, but I will check.

Can you provide me the details of the analog which you posted?

I will try your circuit as well @koraks

Thanks

@koraks I want to try your approach but can you explain a little bit more. Is mosfet require and will voltage increase gradually using pwm?

Just wanted to confirm the possibility of my requirements.

Thanks

Well, you asked for a solution that will allow a magnetic field to be generated in your coil, so that's what it does. It's a pulsed field in fact, but combined with the mechanical construction and the right PWM frequency and duty cycle I expect you could make the needle (that I understand is somehow magnetically connected to the coil) turn to a predetermined position and remain fairly stable there with not too much jittering about.

If you want an Arduino-controlled DC voltage output, you'll either have to drive an RC circuit with PWM or use a proper DAC (or a DAC pin if your Arduino has one; see reply of @killzone_kid).

So let's get this straight - do you need a fairly high-current (few hundred mA) PWM output, or do you need a DC voltage?

I don’t think the OP knows the difference or can make such a decision. But it makes little, all he wants it to do is to just point to a specified number. Either solution will do that.

Yes.

You could use a transistor ( a bipolar transistor to the pedantic ) but a MOSFET is the better choice, because it doesn’t get as hot.

PWM will also keep the temperature down compared to an analogue voltage. The mechanical inertia will stop it wobbling, if not you simply up the PWM frequency.