ADC for relay volume control?

[hegestratos]

Hi,

I recently got my hands on 50 Siemens small signal DPDT relays (V23042), so I want to build an 8-bit relay based volume control. I've read some threads of people building simple systems with a pot and an ADC, or more complicated systems with a ucontroller. I'd like to go for the simple pot+ADC, but I'm wondering about the ADC - I hear the popular ADC0804 (such as used in the Aleph P) is unstable above the 6th bit. I'd like to use 8 bits, since I have the relays. Any recommendations?

Cheers,
Alfred

[mcs]

Why not just use an absolute encoder? There's no reason to use an ADC, as far as I can see.

A microcontroller circuit doesn't have to bee complicated BTW. I have just made this board - only two chips (microcontroller and relay driver).

And third, why 8 relays? I use 6 relays (for 64 1dB steps), which I think is more than enough.

Best regards,

Mikkel C. Simonsen

[TwoSpoons]

I would definitely go for the microcontroller approach. You can do so much more with a bit of software. And hooking up a micro is simpler than using a seperate ADC + glue logic.
e.g. auto mute when changeing source, monitor heatsink temp and wind back the volume if it gets too hot, and my favourite which I thought of today is the parental lock - volume limit for when little Johnny is home alone with your stereo

[kiyull]

I am testing with 12 bit ICL7109(use only upper 8 bit), which is very stable dual slope integration DAC.

Kiyull

[jackinnj]

you shouldn't have any problems with the ADC0804 if you bypass the power supply pins and pay even somewhat careful attention to signal routing -- if Vcc or Vref is noisy you will have problems -- about 5 years ago I made and sold some ADC boards using the chip -- I used a LM4041 as VRef -- I did not use separate digital and analog grounds.

[AndrewT]

Hi,
Sorry to all for going slightly off topic.
Mikkel, can you update your website with the 6 relay version.
Can this be used as a multi channel volume (for outputs of digital filter) control in active speakers?
Is it possible for one microcontroller to serve 6 channels?
regards Andrew T.

[hegestratos]

Originally posted by kiyull
I am testing with 12 bit ICL7109(use only upper 8 bit), which is very stable dual slope integration DAC.

Yes, I thought about that. This should work, but there's still a possibility that you will happen to set the pot so that the output will oscillate between two values. Since you're not using the 4 least significant bits, the chance of it happening is just 16 times lower.

Originally posted by jackinnj
you shouldn't have any problems with the ADC0804 if you bypass the power supply pins and pay even somewhat careful attention to signal routing -- if Vcc or Vref is noisy you will have problems -- about 5 years ago I made and sold some ADC boards using the chip -- I used a LM4041 as VRef -- I did not use separate digital and analog grounds.

I didn't have any problems with the ADC0804 itself in my test setup. But no matter how you wire the circuit, there's always going to be an input voltage where the ADC jumps from one output value to the next. If you happen apply that voltage, the output will oscillate. Obviously, if you reduce the noise in the system, you'll have to be closer to the exact voltage, but it will still happen. Not using the n least significant bits will reduce the odds of it happening by a factor of 2^n.

Needless to say, I'm going for a microprocessor now. I'm aiming at a 7-bit volume control with mute.

Cheers,
Alfred

[BeanAnimal]

With a modest AVR and an endless directional knob (encoder) this could be done.

The ATMEGAS have built in ADC/DAC and control for dallas 1 wire devices. Were talkin a few dollars worth of silicon and a few hours programming. The ULN relay drivers cost as much as the ATMEGA.... but then again you guys have parts bins full of transistors.

Bill