I'm new to the world of Arduino, although not to the world of integrated electronics. I have a basic knowledge of electrical engineering...
I have recently built an amplifier and it's playing happily as we speak. I'd like to built a nice tube preamp to go along with it now, with the following features :
Controlled by a single rotary encoder with integrated push button
IR control
Volume control by means of a lightspeed attenuator (More info)
Input selection using relays
Automatic turn on/turn off if audio detected/not detected for a while (More info)
"Display" status by means of 8x8 RGB led matrix
So my obvious first question becomes, is this possible using arduino?
As far as my googling powers have brought me the first 2 items (rotary encoder and ir control) are 2 widely used features on arduino.
Secondly, for the LDR volume control it seems I could use the scheme used in the "More info" link and simply replace the dual pot by for example an AD5242 and control this from the arduino using I2C.
What is an easier interface for arduino, SPI or I2C?
Thirdly, for the input selection I suppose I simply connect a number of relays to the board (as explained here) and that's that? I have a couple of Omron G5V-2 relays laying around. Would it be better to use a cascading relay scheme, or simply have a relay on every input? What would the impact be on sound quality?
For the automatic turn on/turn off I don't really know where to start... Where exactly, and how, would be the best way to measure it the is any audio being fed into the preamp?
Last but not least, driving the LED array. I'm guessing I will need to use a multiplexing chip here? Plenty of information about that out there, anything specifically someone could recommend to me?
I'm guessing another problem I'll be having is running out of pins on the Arduino...
I found quite unusual to use Si regulator in tube environment design.
Relay is nice. How many inputs are you planning? May be you don't need relay after all, if you o'k with Si, AD5204 / 5206 has 4 / 6 channel, so you can built 2 / 4 stereo input selector (plus it'd allow to mix inputs).
Answer on LED matrix question depends on what kind of status info it'd show?
Single 8x8 isn't enough to print a messages, but more than for on/off status indication
Magician, there will not be any Si in the audio path.
The AD5242 would be used to control the led in the light dependent resistor. The audio path would only pass through the Silonex NSL-32SR2 which is know for being completely neutral and does not change the sound signature.
For the same reason I prefer using relays for the input switching..
I would like to use the led matrix in a novel way. Firstly every led would indicate the volume level, so there would be a resolution of 64 in the volume control. Furthermore the color would indicate the selected input. So for example when the volume is set to 20 and the selected input is 1 then the bottom 20 leds would light up in red. For input 2 the color would change to blue, for input 3 green, etc. I just think this is a nice way than the typical text display and a way to give it a personal touch.
For auto turn off/turn on I guess my biggest question is how wil I detect if there's any input active without putting anything in the audio path.. Any ideas for this??
As you have stated "I have a basic knowledge of electrical engineering..." then you might realize that no active electronic switcing device will be as noise free and distortion free as a relay switching contact. Now whether you can actually hear the difference under double blind testing conditions is another subject.
@Lefty: basic knowledge of electrical engineering does not mean I know how any random digital potentiometer behaves or what kind of audible or inaudible sound signature it has.
If in fact, this does not impact the sound, then it would seem like a better solution. However, I have always been told to try to keep as few components as possible (this IS basic knowledge, no need to make a snide remark on that), and especially silicium components out of the audio path.
The LDR-based volume control is considered as one of the best ways to accomplish this, so that's definitely not changing.
O'K, basically you can drive a leds in volume controlling LDR matrix by PWM output, just filter it out. Or if you wish, leave it to digital pot.
8x8 matrix turn out as 64x1, or just barGraph. Pretty easy to design.
On/Off is not in audio path, it's only touching it in parallel. There is no way you could sense input w/o making connection to it, but I agree that sensing circuitry has to be "non-interfering" high impedance.
Nothing snide meant, just a reminder that the noise floor and distortion differences between a active semiconductor switching component will always be higher then a switch or relay contact. The perfect active amplifier or switching device as defined as a piece of wire with gain has yet to be developed. If you put desired or required numerical specifications to your requirements then more useful help and advice might be obtainable.