**ITS ELECTRIC**
It wouldn't be an electric boogaloo without some electronics and oh boy does this suit have electronics. In one of my previous updates I talked about the power system for my suit, but now I have it really nailed down some I'm going to do a thorough overview of all the little bits and bobs I'm jamming into my brain bucket.
Power Distribution
Our journey starts with two rechargeable USB batteries which will live somewhere in the torso area of the suit, probable the chest. These get plugged into a power distribution board that lives in the chest, which is just a glorified power strip. A similar board lives in the helmet. In my last electronics post these were sloppily assembled with some protoboard. Since then, I taught myself how to use EasyEDA, a free PCB layout program, and had a small batch of them manufactured.
Chest distribution board prototype vs final:
Helmet distribution board prototype vs final:
The two power distro boards are connected with a 4 pin mini din cable. Two of the pins on this cable are + and - for circuit 1, and the two others are + and - for circuit two. Circuit one powers fans, lights and basically any other non-audio electronics and circuit two is entirely audio. This serves a dual purpose, increasing overall battery life, and isolating the audio circuits from electrical noise that is created by the fans. The noise problem is entirely solvable with some decoupling capacitors, but I'm not an electrical engineer and the ripple caused by my fans is
significant so that's a problem to work through once the suit is done. For now, the two circuit solution is working just fine.
Here's how the two boards are connected:
10 JST-PH 2mm connectors are soldered into each board, 5 for each circuit. I didn't add any to the chest board pictured above because I have nothing to power in the chest yet, although I do have some stuff planned (the feature creep on this project has been real). I like the PH connectors because they are reasonably durable (although I wouldn't go yanking on the wires toooo much) and very compact. I add female PH connectors to the + and - leads of all my fans, lights, amplifiers, etc. so they can plug right in. And if I want to move them around, change out a part, or just experiment, no de-soldering or ungluing is required.
Audio
There are two separate audio systems in the helmet: one for talkin' and one for listenin'.
System 1 is pretty similar to
MoeSizzlac's simple helmet speaker system which can be found
here, with a couple of small changes to improve volume and clarity. I had initially planned on using an electret microphone, but wasn't happy with the volume level I was getting. Electret microphones are quite sensitive, so you can't turn your amplifiers up very far before the system starts feeding back. I hopped on Ebay and for about 10 bucks found a microphone designed for handheld radios. This microphone is dynamic which tend to be less sensitive and more directional than electret mics. I also ordered some cheap preamp boards, since the mic didn't have a built in preamp like the electret mic. From the preamp I wired up two little amplifiers, the same ones Moe used I think, and hooked up a speaker to each one. I mounted the grills of the ODST helmet, and crammed the amplifiers and preamp into the right cheek. The microphone attaches to the helmet right in front of my mouth with some velcro.
The talkback system before I added the second amplifier:
Microphone mounting:
Amplifier and speaker mounting:
Speaker grill from the front:
So, this design is pretty loud, but I'm a sound guy and I figured it couldn't hurt to try getting it a little louder. I designed a notch filter centered at the frequency of the feedback I was getting (about 1500HZ), and added it into the signal chain. It does eliminate feedback at that frequency, but is a little too drastic in the way it effects the overall sound. I think I may try designing a little equalizer to put in the left cheek.
The Filter board:
I was going to design the hearing assist circuit myself, but
TheBraus just ripped apart a pair of shooting headphones and shoved it into his helmet and that worked just fine, so I figured why reinvent the wheel. The pair I bought were cheap. The point to point wiring was fragile, and the solder joints were bad, so I replaced it with heavier gauge stranded wire and reflowed all the solder joints.
You can see in this picture that some of the broken connections before rewiring:
Another small problem was that the headphones ran on 3v, and I didn't want to use separate battery pack just for them, so I built an MPC1702 circuit to step down my 5v supply power to 3.3v, and wired that to the power leads on the headphone board.
I drilled two holes in the helmet, one on each side, for the microphones to stick out of, then added extensions to the microphone leads so they would reach. The headphones drivers were uncomfortable so I replaced them with a headphone jack.
The headphone board lives in the left cheek:
As for the fans, those are pretty simple, they just plug in.
Ok, that's all for today. Hopefully I'll have some other cool stuff to show off within the month.
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