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General Category => Your projects => Topic started by: CraXyOW3 on January 22, 2013, 16:07:49 PM

Title: [HELP] Digital Potentiometer to replace regular pot.
Post by: CraXyOW3 on January 22, 2013, 16:07:49 PM
Been googling and searching but did not find anything very useful if not overuse of an arduino.
Doesnt seem prudent to use a complete arduino for this.

My Idea/Question is how to replace a regular pot in a pwm fan circuit for a digital one with tact switches or similar.
Hopefully to have the circuit to remember last used setting.
Title: Re: [HELP] Digital Potentiometer to replace regular pot.
Post by: kam on January 22, 2013, 17:18:02 PM
The problem with arduino users is obvious among new people who want to start with microcontrollers: The arduino has a big board with the programmer and the PSU on board, and a powerful microcontroller. Although this is a very flexible and relatively cheap setup for teaching purposes, it becomes a heavy burdon when one wants to go into more sophisticated circuits.
-- Intro Ends--

What you want to do requires a microontroller, but NOT an arduino. A cheap (less than $1) micro is more than enough for your application. So, invest some money on a programmer for PIC or AVR (arduino carries a programmer for many AVR chips) and start prototyping your own boards. Check the product range of both controller families - You will be astonished by the variety in features AND price.

And then a question pops: Why use such an expensive part to interface a PWM controller for a PWM fan, when you can only use the microcontroller with a fet (or transistor) to interface the fan directly???
Title: Re: [HELP] Digital Potentiometer to replace regular pot.
Post by: CraXyOW3 on January 22, 2013, 19:05:10 PM
That is the thing, i do not want to use something like the arduino at all,imo it's overused.

What i was thinking was something more elegant like the 555 circuit that is presented here, with the difference of replacing the analogue potentiometer for a digital one and having two tact switches for increase and decrease.

I had my eyes on DS1804, sheet -> http://datasheets.maximintegrated.com/en/ds/DS1804.pdf (http://datasheets.maximintegrated.com/en/ds/DS1804.pdf).

But i think im a little out in the blue, hence the question here.

Digital Pot @ Sparkfun (https://www.sparkfun.com/products/10613) - datasheet at site. Microchip.
Title: Re: [HELP] Digital Potentiometer to replace regular pot.
Post by: kam on January 23, 2013, 08:14:18 AM
i didn't said to use an arduino, on the contrary i said to choose the best uC (price-wise). So that you can interface a rotary encoder as well. Anyway.

With the 555 you can achieve either a 1-shop operation or continuous operation. In one shot, the resistance will change every time you press and release a button. A 10K pull-up resistor is connected to the UD. Also, the collector of a NPN is connected to this UD. The emitter goes to the ground. The DOWN button is connected to the base of the transistor through a 4K7 resistor. So, when the UP button is pressed, the UD is HIGH, when the LOW, the UD is LOW.
Now, the 555 is an one-shot circuit. Both buttons (up and down) control the gate of the 555 through a diode (so that they do not interfere each other). The output of the 555 is then driven to the INC pin.

For continuous operation, keep the UD transistor connection the same. Then connect the 555 as a multivibrator. Drive the output of the 555 to the INC pin through a second transistor switch. Both buttons control this transistor switch though diodes.

Again, i do not see anything elegant with the 555 - It is a bulky circuit with many limitations. A uC circuit would be like this: Connect the buttons to an input, 2 outputs to UD and INC, make a software filter and.. end. Plus, you can se the uC to operate with the classic initial delay, you know, when you press a button to  increase the volume, the first click increases once, then there is a delay of 1 sec, and if you keep pressing the button the volume increases once every 200mSec... It is a hybrid of the 2 previous circuits, one-shot and continuous.