As I understand the Arduino Mega can use the PWM pins to generate an analog-out voltage. I would like to produce a voltage output from 0 mV to 8 mV from a designated pin.
Is this possible? And if so, what additional hardware do I need to do to accomplish this?
PWM is not a linear analog voltage. PWM is a variable width digital output with a 0 to 100% duty cycle pulse. The Mega output voltage is 5 volts. PWM can be converted to analog with an r/c filter but an output requirement of 8mv says you’re doing outside conventional usage.
We don't know exactly what you need 0 - 8mV for, or how much of a load you expect to place on this 0 - 8mV source. If it's not much though, something like I've shown in the attached sketch might work for you. You'll need to "do the math" and maybe some experiments to decide what R's and C you might want to use -- but that's all part of the fun! I'd start with R1 = 1K Ohms and C1 = 1uF (or anything close that you might have near at hand), omitting R2 and the potentiometer R3 for the time being while you measure the voltage at the junction of R1 and C1.
Hi,
0 to 8mV is a very small amount to measure in the first place.
What is the application that needs such a near noise level signal?
What will be controlling the level, an input or a programmed process?
Are you trying to simulate a sensor output?
As @CurtCarpenter has suggested with his circuit, you may need to generate a higher more controllable voltage and potential divide it down.
AnalogWrite is a misnomer. The actual output is a PWM signal of approximately 1000 Hz (depends on the board you have).
So it is a digital output that switched on and off 1000 times a second. The average of the output is what you see on a device. For instance an LED. The light output is proportional to the amount of time the digital output is ON.
If PWM is still not clear you should google it. I can't do justice to the subject here.
As I understand the Arduino Mega can use the PWM pins to generate an analog-out voltage. I would like to produce a voltage output from 0 mV to 8 mV from a designated pin.
What bandwidth do you need?
What output impedance?
What level of noise or ripple is acceptible?
What is the reference ground? (Important for low level signals like this which are easily dwarfed by
any ground-loop pickup).
Normally a low-pass filtering voltage-divider would be used (2 resistors and 1 capacitor), if the
low bandwidth / ripple is acceptible. However an output pin can only reference a value relative to
the noisy digital ground bus of the Arduino, not a clean analog ground reference, so this can be
a show-stopper depending on the power supply involved (SMPS is a bad idea here).
It might be better to generate a 0..5V analog voltage first, then use a differential opamp circuit
to re-reference this to the analog ground and then attenuate to 8mV.
The expertise on this forum is amazing and really appreciated. Clearly I am out of my pay grade here. But, I still want to try to make my project.
I am attempting to use the Arduino Uno to simulate the X/Y control of a joystick in a mini quadcopter controller. I measured the voltage change as I moved the joystick forward and back. What I found was the X and Y output voltages were opposite of each other. When X output went from 0 mV to 8 mV the Y output went from 8 mV to 0 mV. If I can get a consistent voltage output from the Arduino then I will disassemble the joystick in the controller and hard wire the Arduino directly. I figure this will allow me to control the mini quadcopter using the Arduino and not my fingers.
So I was wondering if I could use this digital to analog frequency voltage converter and use a resistor on the output to reduce the voltage down to mVs??
Can't be sure kikidog, but I don't think your scheme is going to work.
Many joysticks work by varying a resistor (like the volume control on your radio) which in turn controls the rate at which a series of pulses are produced. The pulses may be very narrow and they will be being produced at a very fast rate. All that means that you really can't measure them with a voltmeter, which will tend to "average" everything -- and the average may be very small (like 0 - 8mv).
Others just close one of four switches depending on where the joystick is positioned. Again, you won't measure much voltage across either a closed or an open switch, except maybe a few mV.
I think you're are going to have to find some more information about your joystick before you can continue your interesting project. You might start by reading this about how joysticks work: The Simplest System: Design - How Joysticks Work | HowStuffWorks .
The expertise on this forum is amazing and really appreciated. Clearly I am out of my pay grade here. But, I still want to try to make my project.
I am attempting to use the Arduino Uno to simulate the X/Y control of a joystick in a mini quadcopter controller. I measured the voltage change as I moved the joystick forward and back. What I found was the X and Y output voltages were opposite of each other. When X output went from 0 mV to 8 mV the Y output went from 8 mV to 0 mV. If I can get a consistent voltage output from the Arduino then I will disassemble the joystick in the controller and hard wire the Arduino directly. I figure this will allow me to control the mini quadcopter using the Arduino and not my fingers.
How did you measure the voltage, for a joystick, that sounds wayyyyy tooo low.
Can you post a picture of the remote and point out where you placed the DMM probes?
Did you use the battery negative terminal as the gnd reference?
All I did was to solder wires to the circuit board pads of the joystick. There are 2 sets of 3 pads, one set vertical the other horizontal. The center pad of both sets of 3 pads is ground. The Y axis of the joystick remains constant at 3 mV. The X axis of the joystick operates in reverse voltage as mentioned above. As the joystick is moved from bottom to top, the voltage of one set of the X axis wires goes from 0 mV to 8 mV and other set goes from 8 mV to 0 mV.
(please note the second joystick has not been tapped yet. You can see the vertical/horizontal pads on the left side of the image.)
I was planning on removing the joystick all together and using the Arduino to simulate the low voltage.
I would purchase a PWM to 0-10 Volts module to generate the analog voltage. Once I have the PWM converted to output 0-10 Volts couldn't I just use a voltage divider (resistors?) to reduce say 2 volts to 2 mV?
I was thinking of using small power supply to produce the 0-10 volts to drive the voltage divider to verify the correct mV output I need is generated. Then connect it to the joystick controller circuit board. It should operate the quadcopter as if I were moving the joystick. Once that was working sufficently I would then innterface the Arduino.
The quadcopter I am using is this one:
The joystick controller does not seem very sophisticated. I really think the hardest part is to get the voltage down to mV.
Sorry for rambling on with all the gibberish, just trying to provide an overall picture of what I am doing.
Hi,
Try using the battery/power supply negative as ground, and measuring the centre pin DC voltage of each joystick pot.
In other words always reference voltage measurements with respect to negative, because what ever you use to imitate the joysticks will also be referenced to the battery negative.
Thank you very much TomGeorge! You were absolutely correct. I was metering the joystick controller incorrectly. I tried your way and the volt range jumped to 0-3.33 volts. However, I had to completely remove the joystick from the controller pc board and only connect to the middle wire I added and the negative leg of the battery box. And after writing some code and purchasing a PWM to Analog module, I was able to initialize the controller and have the quadcopter take off! However, it flew around all haphazardly. The quadcopter is too small to add bluetooth and a gyro to stabilize it. Darn!
So, I guess, thank you very un-much TomGeorge. I now have to consider spending more $$ for a bigger quadcopter. (Seriously, thanks again TomGeorge) I will keep you posted.
The expertise on this forum is amazing and really appreciated. Clearly I am out of my pay grade here. But, I still want to try to make my project.
I am attempting to use the Arduino Uno to simulate the X/Y control of a joystick in a mini quadcopter controller. I measured the voltage change as I moved the joystick forward and back. What I found was the X and Y output voltages were opposite of each other. When X output went from 0 mV to 8 mV the Y output went from 8 mV to 0 mV. If I can get a consistent voltage output from the Arduino then I will disassemble the joystick in the controller and hard wire the Arduino directly. I figure this will allow me to control the mini quadcopter using the Arduino and not my fingers.
No, you are misunderstanding what's going on. This is classic xyproblem example: xyproblem.info
The joystick will be getting much larger voltages than that, otherwise the controller would be plagued
by noise sensitivity issues.
What its doing is switching on the power to the joystick pot on a regular basis, measuring the pot wiper
voltage, then powering down the pot till next time. Thus the average voltage is small (multimeters average
over long time periods of a second or so), but the actual measured voltages are several volts.
Its probably multiplexing both pots in fact.
An oscilloscope is needed to further figure out the actual details - it may not be so easy to fool this device as you hoped.