I'm working on building a passive attenuator for use eventually as a simple Arduino-controlled volume controller. I've found a similar schematic called the RelaiXedPassive Attenuator. It uses an attenuator ladder arrangement, using 6 relays to provide 256 steps of attenuation. I've started assembling it and testing it out with strange results, and I'm trying to determine what exactly I'm doing wrong.
Here's the schematic I'm working off of (page 1, specifically). From what I understand, it has 6 stages, each with a relay that either sends the signal through a voltage divider or bypasses it. All bypassed = full audio volume, All on = no audio, and 254 other values in between.
Here's what's going wrong:
When I mock up a couple stages, audio goes through fine, but the difference between the first stage on and off is drastic – it's about half the volume. This is just the first stage, though, which should be the least amount of resistance. Why the huge jump? Looking at the circuit, it does makes sense...The signal is going through R202, a 2700Ω resistor. In fact, it seems like this isn't acting like a voltage divider circuit at all...When I remove R204 and leave pin 7 (9 on my drawing below) of the relay floating, it makes no difference to the sound at all. Those resistors seem to be doing nothing.
Here's another view of the ladder arrangement, which I got from the same site's attenuator calculator. It's unclear to me what the entire bottom row of resistors are meant to achieve, as they do nothing to the sound of the audio when I remove them.
Here's a very specific schematic I drew up of exactly what I've mocked up, in case I'm misreading something:
R204 and R206 seem useless to this circuit.
Just to be clear in the above drawing, I'm manually toggling pin 1 of the relays between 5V and GND to turn them on and off – that part is working fine.
Did I do this right? What am I missing here?
Thanks for your help!
Here's the schematic I'm working off of (page 1, specifically). From what I understand, it has 6 stages, each with a relay that either sends the signal through a voltage divider or bypasses it. All bypassed = full audio volume, All on = no audio, and 254 other values in between.
Here's what's going wrong:
When I mock up a couple stages, audio goes through fine, but the difference between the first stage on and off is drastic – it's about half the volume. This is just the first stage, though, which should be the least amount of resistance. Why the huge jump? Looking at the circuit, it does makes sense...The signal is going through R202, a 2700Ω resistor. In fact, it seems like this isn't acting like a voltage divider circuit at all...When I remove R204 and leave pin 7 (9 on my drawing below) of the relay floating, it makes no difference to the sound at all. Those resistors seem to be doing nothing.
Here's another view of the ladder arrangement, which I got from the same site's attenuator calculator. It's unclear to me what the entire bottom row of resistors are meant to achieve, as they do nothing to the sound of the audio when I remove them.
Here's a very specific schematic I drew up of exactly what I've mocked up, in case I'm misreading something:
R204 and R206 seem useless to this circuit.
Just to be clear in the above drawing, I'm manually toggling pin 1 of the relays between 5V and GND to turn them on and off – that part is working fine.
Did I do this right? What am I missing here?
Thanks for your help!