Sound System Work

It had a busy weekend, but I did find some time to work on R2. I decided to continue focusing on the sound system and electronics in general as it’s easier to start and stop with minimum mess and cleanup.

I did hear back from ACS about the specs on the internal amplifier in the CF3 sound system. It turns out I was right and it can deliver 25W per channel, or 50W total. Their manual is rather vague and states it can only do 20W total, so I’m glad I checked now. I bought some new generic 4 1/2″ 4 ohm 30W speakers to test and they sound pretty good and seem louder and clearer than the single 15W horn speak I was using. Each speaker is connected to it’s down channel and delivers more sound than my ears could handle comfortably. I’m probably going to mount them behind the front vents for now, but may end up moving one into the skirt to bounce some sound off the floor to help it travel further and in more directions.


With the speakers out of the way I started to think about how I had the electronics laid out. Some of you may remember this is what my original electronic mounting panel looked like for C4.

It’s worked great, but I need to add a few things and as it stands, once the skins go on, I think it will be hard to use the hinged electronics panel to get access to the internals of the droid for maintenance, e.g. the batteries. I’m thinking it maybe simpler to move some or all of it internally to the droid.

With that said I started to disassemble the rear panel. I needed to do it anyway to add the Contact 24 I/O daughter card to the CF3 sound system. This will give me more options on the range of sounds I can trigger.

I’d been putting this off for a while as everything was working okay, and I could sort of live with only being able to trigger two banks of random sound vs the possibility of twelve banks.

With the everything disassembled adding the daughter board to the CF3 was a snap.

While I had the CF3 open I wanted to add an external connector to the white 3 pin header which bring out the volume control. It’s located just below the new Contact 24 daughter board and next to the CF card slot. I plan on connecting it to 2 channels on an RF receiver/relay board to allow me to adjust volume remotely.

3 pin volume header

The plug is pretty standard and I ended up buying a $2 fan extension cable as I couldn’t find loose plugs locally.

But there was a slight problem, the plug is too long and stops you from putting the Contact 24 card back in it’s place so I had to chop down the plug a bit.

I drilled a hole in the side of the box for the wire to pass through

I temporarily wired up the three contacts (up, down, common ground) to my RF receiver to try it out and it worked first time which surprised me. The plan is to have the volume on it’s own RF remote as I wanted to keep all 12 channels free on my original RF remote just to trigger sounds.

Now that the Contact 24 board was in place, I could start wiring up all 12 channels to the RF receiver using some hacked-up twisted pair LAN cable I had laying around.

Basically all the connectors labeled “A” on the RF receiver are connected to the adjacent “A” and then over to the common ground on the CF3 sound system. Then I connected the “B” connector of each relay over to a contact on the CF3. Starting at the top left going down is relay 1 thru 7, then on right starting at the bottom going up is relay 8 thru 12 . Each connections maps over to contacts 1-12 on the Contact Sense 24 board in the CF3.

RF Receiver wired up

This is the CF3/Contact Sense 24 side of the wiring. Each block of green plugs/connectors has 10 connections. The outside two are common ground. I’m only using one from each block and routing it over to the the two halves of the remote relay board (brown wire)

CF3 Connections

Here’s the the connections on the smaller 4 channel RF Receive from the CF3 volume cable. Note that on the 4 channel receiver we’re using connections B and C instead of A and B. This caught me of guard as the documentation that comes with the board is incorrect.

I’m going to Velcro each of the RF Receiver to the top of the CF3 case.

Right now I have the two RF remotes Velcro’d to the side of my transmitter, but I’m tempted to create a small box with better switches on it similar to the Vantec KeyCoder and have the RF transmitters hidden inside.

And finally here’s a wiring diagram I created that will hopefully make things a little easier to understand. There’s also a PDF version for printing.

CF3 and RF Remote Wiring Diagram

Next step is to reprogram the CF memory card to use all 12 channels of the remote.

Posted by Chris on December 17th, 2007 in Electronics | Comments Off on Sound System Work

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