need a wireless volume control

[Peter Pan]

I need a wireless remote volume control. The transmitter / control has to mimic an ordinary rotary control too, and has to be a pretty small battery operated deal since it's going to be mounted on a guitar. It also has to be RF, since line of sight (IR) won't cut it. I'm pretty sure I'm going to have to roll my own herem but maybe some of you have some ideas. Even something I could start with and modify.

[DUG]

Well, there are many ways to do this.

One way is to use a PIC or microcontroller to monitor the position of the control pot and transmit any changes it sees. This will keep the transmitter activity low and save on battery life. The transmitter section should have a standby mode for low battery drain as well.

The receiver could be done a number of ways.

One is to receive the data and control a buffered pwm output (easier than D-A) to DC control a volume control IC. (like a LM1036M/NOPB)

This way you will have a linear pot control a log volume control of > 70dB.

Not easy but it should work.

Is this what you were thinking of?

[Peter Pan]

Well maybe! Those are good ideas. I had also thought of gutting a mouse and making a rotary control, employing the patterned wheel for one axis along with the its pair of light sensors. You know., the patterned wheel interrupts the light between two LED to Light Sensor diodes, and provides both counts of movement as well as direction information. So now if I started with a wireless mouse, then theoretically I'm half way there. But taking the other side, which likely has a processor and is hard coded to translate mouse coordinates into and through a USB port, would not be an easy hack. On the other hand, it might be true that a wireless mouse is common enough that chip makers such as TI already make some DIY interfaces. And if not, even just starring with the patterned wheel and sensor principal might get me started. For example, if I could use the two sensor outputs to trigger tones on a DTMF chip and transmit that to a receiver, I ought to be able to decode the tones at the other side with a similar chip, and then use a PIC chip or discrete logic to convert the count and direction info to drive an up/down volume control chip.

Funny you mentioned the PWM though! Don't laugh, but it crossed my mind that PWM is the way hobby servos work. So a pot controlling the duty cycle of a square way that is somehow transmitted over an RF link (perhaps old fashioned FSK over RF) could be decoded back to a PWM at the receiving end, to drive a hobby servo and receiver. So whats so funny? The fact that after all that, I'd consider connecting that hobby servo to a slide potentiometer, to accomplish the remote volume control.

OK, that's a Rupe Goldberg, and I guess there are a million ways. The tough nut for me is the transmitter and receiver though. I stink at RF design, and I wouldn't want something horribly suseptable to interference. So I guess I was hoping to find some low power (and low price) RF transmitter and receiver building blocks.

[DUG]

Take a look at:

rf-solutions.com: The Leading Resolution Site on the Net

(Stocked at Newark and probably others)

Stay away from PWM as the data slicer (decoder) will have trouble with continuous 0% or 100%. Unless you use delta from 50% as an up-down signals to the volume control.

A data burst type structure would be better for battery operation.

The wheel from a mouse would give you up-down and pulses. You could use that for tone generation with the DTMF decoder. I like that idea.

Research, research, research

[Peter Pan]

I'm not sure I understand that rf-solutions link Dug. It seems that you can click three or four levels down and just get more lists of categories, and it almost seems more of a collection of links harvested from search engines than a real compilation of products. Did you have a particular product link recommendation for the radio link part of this?

[DUG]

Sorry about that.

I thought that rf-solutions was a real company. (Faulty memory cels)

Try to search for rf modules in Mouser or DigiKey.

Use these rf modules as building blocks.

[raudio1969]

I think your project is interesting. For the RF link, check out Linx Technologies.

Home | Linx Technologies: Wireless made simple®

Best regards,

Richard

[DUG]

"For the RF link, check out Linx Technologies"

Yes, that was the other one I was trying to remember.

[Peter Pan]

Thanks guys. Short rant: Very frustrating is to see so many ultra small and ultra cheap 2.4 ghz modules on e-bay, all from China suppliers, only to not even get a single answer to 14 inquiries to track down a bit of documentation. Oh well... that's part of the drill.

Anyway, I'm looking into the Linx technologies site now. I also found these products..

433MHz RF Remote Control System

They are only 433 mHz, which could mean needing a visible antenna, but the encode/decode chips and interfaces look interesting. I don't know what they are but from the diagram I gather that they are just memory chips with serial I/O, where on the transmit side the 8 parallel data bits are directly read in, and apparently fed to the transmitter as serial data. A similar thing is done at the receiver side in reverse. I've done slightly things like this in the past, using a programmed memory chip as an encoder/decoded, bout only as a MUX (like converting 4 parallel bits to 8 or vis/versa), but never with a serial I/O memory chip. I've written to the company hoping the same principal might be applied to a higher freq (like 2.4 Ghz ) transmitter, but any guidence on what exactly is going on there would be appreciated.

Anotherr little hitch here. As I said, I know that I can gut an old mouse and build up my own one chip quadrature output circuit, but it sure would be nice to find an existing self contained control for that part, in case i ever decide this is a good enough idea to market. I was encouraged to find a link to a message someone wrote about having found exactly what I'm looking for for just a few bucks...

Nice inexpensive optical encoder found - Arduino Forum

But of course it was a 2 year old post. The place he got it (bgmicro.com) doesn't have them anymore. The original part and similar ones are available (Electroswitch 900 Optical Encoder Series), and can be had from mouser fro about $55. This is a tease i can't bear! These units look and feel just like a high quality volume control, and apparently all you need do is apply 5 volts, and you get a nice 2 bit quadrature output when you turn it. Does anyone know of a similar unit I can get as some kind of inexpensive close-out?