[sdiy] wireless patching

[rsdio at audiobanshee.com]

My point is that the original question did not assume PWM already existed, or even digital.

The original question concerned wireless modular linking of analog CV. Quincas asked whether a uP and ADC were necessary, or if there was a simple analog way to do it. I don't know of a simple way to create a PWM signal from an analog voltage (although I'm not assuming it doesn't exist just because I don't know about it :-)

It could be more trouble to create PWM so that you can use RC, rather than simply use FM via some other method.

The latency that you complain about in a digital word protocol would not necessarily be worse than the 50 Hz update rate of the RC solution. That's a 20 millisecond latency right there for the RC method. In that length of time, a 100 kbps digital protocol could transfer 2,000 bits, which is more than enough bandwidth for 8 channels of 16-bit words. I'm thinking that a digital protocol would actually be lower latency than RC updates.

Another issue is that the RC solution is limited to a 50 Hz sample rate, whereas the digital word protocol could manage a higher sample rate - maybe even 16 times the sample rate. Fortunately, the RC solution does seem to sample all channels at 50 Hz, but that's a fairly low limit.

Brian


On May 25, 2017, at 11:43 PM, Roman Sowa <modular at go2.pl> wrote:
> PWM is digital output, so what's your point?
> Using digital words over this radio module would require much higher bandwidth, they usually are limited to 100kbps, sometimes much less. Higher bandwidth models don't have keying input but take SPI or I2C, packetize it and send embeded in some protocol, sometimes with 2-way link. That creates latency.
> 
> As Matthias just said, this is what RC control uses, TDM-ed multiple PW. This is the best solution I think. One visit in RC store and your wireless connectivity project finished, just add filters to servo outputs of the receiver, as their output is PWM.
> 
> Roman
> 
> W dniu 2017-05-25 o 22:52, rsdio at audiobanshee.com pisze:
>> FSK and ASK both assume digital input. If you want to send analog
>> data, then you should be able to use standard FM, which can transmit
>> analog signals. So long as the pilot frequency and the signal
>> frequency survive the transmission, you should be able to reconstruct
>> the analog signal on the receiving end.
>> 
>> I do think that multiple CV would require multiple transmit
>> frequencies and multiple receivers, though, to keep the signals
>> distinct. That would be true with ASK/FSK or straight FM.
>> 
>> Brian Willoughby Sound Consulting
>> 
>> 
>> On May 25, 2017, at 2:29 AM, Roman Sowa <modular at go2.pl> wrote:
>>> BT is no good for realtime. How about really simple $2 RF modules
>>> that have FSK or ASK input? Not sure if you can freely modulate
>>> with any PWM signal or is it quantized to some fixed data rate, but
>>> common sense tells me that the simples cheapest module just drive
>>> the radio directly. So you have wireless PWM link, and that's just
>>> one step from CV.
>>> 
>>> Roman
>>> 
>>> W dniu 2017-05-25 o 01:13, Quincas Moreira pisze:
>>>> Hey friends! If you were to design a fast and precise wireless
>>>> transmission and reception system for eurorack, how would you doi
>>>> it? Synth 1 > ADC > uP
>>>>> Bluetooth > uP > DAC > synth 2 ?  Or is there a simple analog
>>>>> way to
>>>> do it with RF?
>>>> 
>>>> I mainly want to send control signals, but as we know, those can
>>>> be up in the audio frequencies or higher!
>>>> 
>>>> The idea is to have like, 4 systems set up on 4 corners of a room
>>>> and inter-patch them without stretching long cables all over the
>>>> place. I think 8 sends and 8 receives on each remote patch box
>>>> would suffice, and some system to match sends to receives.