Stainless steel conical beer fermenter Pt.8

The beer fermenter project is finally ready for its first batch of beer. I bought a soft silicone strip from McMaster and cut a scarf joint in it. The diameter of the finished ring matches the lid on the fermenter.






I did some testing and verified that standard silicone adhesive would bond the red silicone rubber strip very well. I am pretty sure that if tested to destruction, the glue joint would break before the rubber itself would, but it still seems tough enough for this application.

I also welded my stainless cooling coil into the lid.


I made some Delrin clamps to keep the lid held tightly onto the tank. The silicone rubber is very soft which helps easily make a seal with minimal clamping pressure. I clamped it all up, shut both valves, and sucked some air out with my lungs. I could feel the vessel holding the vacuum that I created, so I assume the setup is essentially air-tight.

OK, so now it's time to brew some beer! Any recipe suggestions?

Installing Bluetooth audio in my car with a Motorola s705

I am nearly done with my project to create a seamless way of playing music that is stored on my computer in my car. I bought a Motorola s705, which is a Bluetooth audio receiver with headphone jack. It is capable of operating as a standard phone headset and also capable of receiving high-quality audio. First, let me review the s705 itself:

I easily paired the s705 with my HTC G1, and was able to play music through the s705 with no trouble. The sound quality was extremely good -- significantly better than the G1's own headphone adapter. It appears the high-pass filtering that the G1 uses on its own audio stream are thankfully not also used on the bluetooth high-quality audio stream. I could not hear any compression artifacts, and the sound quality remained top-notch as I walked up to about 15 feet away from the phone. I did not test the s705's battery life. I accidentally turned on the FM radio a few times, and I wish that feature could be disabled. The only negative thing is that the s705 and G1 sometimes do not connect to each other after being separated, then brought back together. Sometimes, they will only establish a phone audio connection and not a high-quality (A2DP) connection. Turning the phone off and on (or going into airplane mode and back) always fixes the problem. Turning the s705 off and on sometimes fixes the problem.



So after I decided the s705 would probably do the job, I took it apart (of course). I needed a way to remotely control the s705 power (to have it turn on everytime I started the car, and off when I shut car off), and also a way to allow it to charge its own battery while not running the car battery down.

In order to turn the s705 on or off, the power switch must be held down for three seconds. One side of the power switch would go high (about 4 volts) when the switch was pressed. Thus, I could control the device's power state by sending it a 4 volt pulse that lasted three seconds. My first plan was to use an Atmel AVR microcontroller and use a feedback circuit so that the AVR would know whether the unit was on or off. I had difficulty finding a reliable logic signal on the s705 circuit board that could be used as an on/off indicator. I was also having difficulty with the Atmel IDE that night, so I scrapped it, and decided to use two basic timer circuits (a 555 and 558 chip). The circuits send a pulse when the car turns on, and another pulse when the car turns off. It's possible for the device to become out of sync, but I don't think it will happen. The circuit uses a MOSFET whose gate is driven by a capacitor-resistor network and charged by the "on" signal from the car stereo. This way, the device will draw essentially zero current after the gate discharges and the MOSFET turns off. I've configured the capacitor value so that the circuit stays powered for 15 seconds after the car turns off.


I also wanted to sneak the audio wires out the back of the unit instead of using the headphone jack on top. I figured this would look a lot nicer when I mounted the unit on my car's dashboard.




I used the s705 shirt clip to attach it to an unused switch plate in my 1992 Honda Civic. It fits right next to the rear defroster switch.

The row of header pins have the following signals:
1. gnd
2. +12V always on from the battery
3. +5V signal from car stereo when the aux input is active
4. audio signal gnd
5. audio left
6. audio right

The audio connections go to my car stereo "aux input" which I described in another post:






The shirt clip was ABS plastic as was the switch dummy plate. I used some Weld-On #16 glue which will very securely bond ABS plastic.

It's a pretty clean installation. I've just finished it, and I'll let everyone know how it works in day-to-day use. So far, my tests in the driveway have been really great -- just step into the car and turn on the stereo, hit play on the s705, and the music starts. I don't even have to take the phone out of my pocket.

Adhesive for polypropylene and other low-energy surface plastics

I recently had the task of gluing two pieces of polypropylene plastic together. It sounds easy, but polypropylene is a plastic with very low "surface energy" -- meaning it's difficult for most adhesives to "wet" the surface and make a good bond.

This problem of not being able to wet the surface can be seen when dripping water on a recently waxed car. The water forms beads and quickly rolls off the surface. If the car's surface has not been waxed in a long time, the water droplet may stick to the surface and form a sheet or stream of water flowing on the surface. The difference is that the wax provides a much lower energy surface to the water, which has a difficult time sticking to the wax and forms a bead and rolls away.

Plastics with low surface energy (polypropylene, polyethylene, etc) are used for food containers and other vessels because of their mechanical properties and also their inert surface that allows liquids to easily roll off. So, how to glue them? I searched the web and found this product:

3M Scotch-Weld DP8005. It has some magical composition that allows it to wet very low energy surfaces.


It's pretty expensive -- a little over $20 at McMaster, plus the special plunger (another $8). The tube of adhesive and plunger are intended to be used in a dispenser that works like a caulk gun. They also sell a mixing tip that swirls the two parts of the adhesive before dispensing. That's all fine, but I prefer to just mix with a nail on a piece of paper. I bought only the tube and plunger and had no difficulty dispensing, mixing then applying with a nail.

The adhesive itself is pretty weird. It's gritty, like it contains tiny glass beads or sand. I applied the adhesive to my project (polypropylene bottle and flat slab of polypropylene), and put the pieces with very light clamping pressure in an oven at about 80*F for about six hours. I shut off the oven and went to bed. The overnight temperature in my shop was probably 50*F.

The next day, I took the parts out of the oven and was glad to see the adhesive worked very well. It made a very strong bond -- strong enough for me to drill and tap two holes with 1/8" pipe threads in the 1/4" thick slab that I glued to the bottle. The plastic showed no signs of coming loose. I made six bottles like this, but didn't have a spare bottle for destructive testing.

DIY aux input cable for Kenwood car stereos

In order to achieve my master plan of abandoning CDs and converting entirely to digital/wireless music, I need to get an audio stream into my car stereo. It is a Kenwood kdc-mpv619. The front of the stereo has no input jacks. The back has output RCA plugs, but no inputs. The only way to get a signal into the stereo is to use the CD-changer connector. This is a 13-pin DIN connector that contains pins for the audio signals as well as CD changer control signals. Around the year 2001, Kenwood realized that people wanted to use the connector for aux input and started to sell an adapter ( CA-C1AUX ) to convert the 13-pin DIN into a pair of RCA input jacks. Prior to 2001, Kenwood models would not accept audio on the DIN connector until it had established digital communication with the CD changer. I know this because I had to get a CD changer and hi-jack the audio lines for an older Kenwood stereo that I have. Anyway I made a copy of the C1AUX adapter, and also helped myself to the power lines that are supplied in the DIN connector.http://pinouts.ru/Home/kenwood_head_pinout.shtml

The resistor is necessary to indicate that there is something connected, and that the stereo should make "aux" available in its menu of input selections.



So, it all worked fine, but the sound on the G1 was still horrible. No bass. No treble, but there didn't seem to be much distortion. It actually sounded pretty clean.

The next step will be to use a bluetooth receiver to feed audio into the car stereo.

Making twisted wiring harnesses with a hand drill

My dad learned this trick from a stereo installer when he worked at a Honda dealership. If you use similarly-sized wires, the resulting twist pattern is very uniform and professional-looking. Cut off a bunch of pieces of wire, then stuff all of the ends into a the drill chuck and clamp it down. Start the drill turning, and use your other hand to keep tension on the wires.

In this case, I made a wiring harness with a stereo audio cable and two power conductors.