Help with low cost digital wireless mike transmission - Page 1
Forum section: electronics / projects

author: vk3pb
author_rank: Contributor
timestamp: June 08, 2014, 04:03:34 am
content: Hi Dave, allI would be grateful for some help with a low cost digital hack I am working on. The idea is to create a low cost way of transmitting audio from your dynamic mike to your camera input or sound card input.The problem.I hate cables. They are the bane of my life. As I help make a podcast I am continually using a Shure PG-48 mike with a long cable. It would be far more convenient to have some sort of wireless link instead of my mike cable. The problem is that commercial solutions like those sold by Heil can easily top $100. Why pay more when you can hack?The possible solutionI came across the following web page which discussed interfacing a usb sound card to decode and encode audio for 433 mhz digital transmission and reception. This made me think - could I build what I wanted using a 433 mhz transmitter/receiver pair and a couple of cheap usb sound cards?http://rurandom.org/justintime/index.php?title=Cheapest_ever_433_Mhz_transceiver_for_PCsI'd like to give it a try but I have once concern. How do I interface the audio input on a usb sound card to the xlr connector on a Shure PG-48 mike? Does the mike require 48v phantom power and if so to which pins should this be applied? If anyone can suggest a simple circuit that would be greatly appreciated. Perhaps Doug Ford from Analog design might be able to suggest something? By the way this design is not intended for commercial use - I just want to build this and then feature it on my podcast for open source hardware use.The transmitter/receiver combination I propose to use is herehttp://www.futurlec.com/Radio-433MHZ.shtml(I would use the RFM-02 and RFM-01 combination.)Cheap USB sound cardhttp://www.ebay.com.au/itm/USB-2-0-Audio-Headset-Headphone-Earphone-Mic-Microphone-Jack-Converter-Adapter-E-/251517968415?pt=AU_Components&hash=item3a8fa3a01fThanks Peter

author: TVman
author_rank: Frequent Contributor
timestamp: June 08, 2014, 04:41:51 am
content: Try the eRIC.http://www.lprs.co.uk/[/

author: vk3pb
author_rank: Contributor
timestamp: June 08, 2014, 05:01:23 am
content: >Try the eRIC.>http://www.lprs.co.uk/[/More expensive than a Heil solution unfortunately.

author: Rigby
author_rank: Super Contributor
timestamp: June 08, 2014, 05:07:09 am
content: Seems like an analog radio transmitter and USB SDR could get you there for very little.

author: vk3pb
author_rank: Contributor
timestamp: June 08, 2014, 11:16:01 am
content: I wouldn't be able to use a usb sdr with my camera which has a 3.5mm mike jack so that is out.

author: Legit-Design
author_rank: Frequent Contributor
timestamp: June 08, 2014, 11:46:29 am
content: Quote from: vk3pb on June 08, 2014, 11:16:01 amGet one small fm radio use simple cable to get it into 3.5mm and make one of those car fm transmitters battery powered if you can't find one already made. Back in the days small fm radios for headphones were everywhere. Those car fm transmitters take in 3.5mm plug.

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 08, 2014, 12:55:30 pm
content: Many of those analog video senders can transmit a S/PDIF signal with no modifications.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 08, 2014, 02:00:31 pm
content: Shure PG-48 is dynamic and does not require any power, neither phantom power (48V) nor "plug-in power" (~5V). Professional "body pack", clip-on lavaliere ("lav") mics like the one that Dave uses, typically use small electret condenser mics that require a low-voltage to operate the internal impedance converter FET. That voltage is provided by the "body pack" transmitter box. But dynamic microphones are completely passive and do not require any external power.Most of those small, inexpensive wireless transmitter/receiver products are designed for data (binary) signal communication. Some of them may be hackable for analog (audio) signal transmission and reception. But squeezing decent audio performance out of them would be a MAJOR task, IMHO, and quite possibly even more difficult than doing the transmitter and receiver from scratch.Sparkfun had an FM transmitter module for audio in the pasthttps://www.sparkfun.com/products/retired/8482but it was not very popular, and they dropped it as a product for sale. But they still have receivers likehttps://www.sparkfun.com/products/10663andhttps://www.sparkfun.com/products/11083However, there are perhaps hundreds of simple (1-2 transistors) FM transmitter circuits available out there on the interweb. And even some more sophisticated designs using more modern chips like MAX2606, etc.Then there is the old standby, BA1404 chip for making FM transmitters, or the more recent BH1415F. Here is a $10 board on Ebay using the BH1415F:http://www.ebay.com/itm/261072882221And there are many similar transmitter and receiver modules on Ebay, etc.But, honestly, even using a transmitter and receiver board-level module seems pretty fiddly to me when for LESS money and LESS time and LESS fooling around, you can get ultra-low cost wireless mic kits (transmitter/receiver) that have the finished transmitter and receiver modules integrated together. For example:http://www.ebay.com/itm/151149031635

author: David_AVD
author_rank: Super Contributor
timestamp: June 08, 2014, 10:05:55 pm
content: Quote from: Richard Crowley on June 08, 2014, 02:00:31 pmNo mention of the wireless frequency used on those sets. The OP doesn't have a country flag set so hard to say, but keep in mind that there are wireless mics being sold that are in unsuitable bands. For example, in Australia at the end of 2014 it will be illegal to use wireless gear in many of the old bands due to the sell off of the spectrum. More detailshere.

author: fcb
author_rank: Super Contributor
timestamp: June 08, 2014, 10:22:35 pm
content: Nordic Semi make the nRF2460 and nRF24Z1 (http://www.nordicsemi.com)The latency is not that low (20ms min, but that might not be an issue), interfacing to an ADC/DAC is a piece of cake. If you wanted more dynamic range, then you could probably split 24 bits between the two stereo channels (CPLD required).Their stuff (Nordic) is pretty good, available and there are dev. kits for alot of the stuff.

author: vk3pb
author_rank: Contributor
timestamp: June 09, 2014, 02:07:48 am
content: Thanks for the replies.Some interesting ideas. I already have wireless condenser mikes and i get a lot of hiss on them.I should point out that I am interested in getting good audio out of any hack I can produce. The reasson I chose the particular 433 mhz transmitter/receiver combination is (a) to avoid the congested 2.4 ghz band band and (2) the particular model of transmitter/ receiver combination I have chosen allow 115k of data thoroughput which should be enough for good sound quality. The limiting factor would be the sound quality of the usb sound card. Hopefully its something better than 4 khz