I was able to get the engine stand completed and engine running again.
The old exhaust system was pretty much cracked and fell apart when I tried to remove it from the three wheeler so I had to make a “new” setup. I bought the cheapest muffler I could find on eBay ($15 moped muffler) and some spare steel tubing I had and I welded up a temporary exhaust. I reused the old exhaust flange that mounts to the engine but I would like to replace all of it with new material when I finally transplant this engine in the go cart.
I then mounted the fuel tank I bought on ebay for $6. Fairly tiny with only 1L of capacity but the tank was pretty cheap and doesn’t leak… can’t complain about that.
I made the fuel tank mount out of some old aluminum sign material I had forever. I think I have been holding onto that material for over a decade now! Knew it would be useful some day :)
The fuel tank mount is designed to be unscrewed giving me more access to the engine when I start disassembly.
And it fired right up after filling the tank up. Glad I got the wiring right!
What is next is to disassembly and clean the entire engine. Once it heats up it smokes pretty good so I will need to at the minimal replace the piston rings and lap the valves. Probably end up honing the cylinder walls for the new rings.
Those that listen to my podcast know that I enjoy working turning wrenches on vehicles and engines. Before my friend Stephen moved to Colorado he dropped off his old Honda ATC110 3 wheeler. It was in pretty bad shape. The drive train was all twisted up from when the chain fell off and jammed up. Fenders where cracked and the front fork was tweaked a bit. Only good thing was the 110cc engine fired up right away.
This gave me an idea. When I was younger I always wanted to build a go cart but never had the funds, tools, and my parents where very wary of the idea. Now I have a perfectly good 110cc engine, a welder, and no longer under the supervision of my parents :) .
After a couple 11mm and 14mm bolts the engine was freed from the old 3 wheeler chassis. Time to get rid of the old chassis and parts I am not going to use.
I looked online and these chassis’ don’t really sell and would be a pain to get rid of otherwise. A sawzall and cut off wheels made quick work of the pressed steel chassis and tubes.
With some scrap material I had left over from other projects, I fabricated an engine stand for the 110cc engine.
I then wired up the various electrical bits of the engine. These engines have very little electronics to drive them. An alternator generates the power for the sparkplug which is controlled by the CDI (Capacitor Discharge Ignition unit). I found the wiring diagram for this engine here.
On the other side of the engine stand I mounted the throttle and ignition coil.
What is left on the engine stand to build is an exhaust system and adding a fuel tank. For the exhaust I found a $15 mini bike/moped muffler and some 1″ 16AWG steel tubing. The fuel tank is a $6 plastic mini bike tank. Next update on this project I hope to have those installed and the engine running on the stand. This engine needs a complete tear down as it leaks from every seal and I would rather not get my new go cart all oily!
I have been working on my old 1999 TJ Jeep and I always wanted to have Bluetooth connectivity in for the stereo. I could have bought an after market head unit but I never really liked the look of them and they tend to be easily stolen out of the Jeep (softtop!). The stock head unit matches the dash and is less likely to be taken. Thus the solution was to hack in a Bluetooth module into the radio!
First I bought a used radio on ebay. Part number for the radio was P56038933AB and I was able to pick one up for $25 as I wanted to keep my radio functional in the Jeep till I got the Bluetooth working. Then I picked this module on amazon. I chose this module as it had a wide input voltage, every single connection and signal was brought out to a header, and it had good reviews.
Next I opened the radio. It had T15 Torx (jeep thing :| ) machine screws that held it all together. Took it apart all the way to the bare radio.
Next to figure out how to get the Bluetooth signal injected into the radio! Most people that do these kind of hacks just blindly poke around the radio till they find and audio signal and then inject there. This is fine but I wanted to make sure I was getting the best audio quality out of my cheap Bluetooth module and early 90’s designed, base model head unit. I also wanted to keep the volume knob on the radio functional. This meant injecting the Bluetooth signal in the circuit before the power amplifiers and before it was gained for volume.
To figure out where to inject the audio. I first wrote down all the IC Manufactures, Part numbers, and Package size. Clicking the links will show an image of the IC.
Next I started searching for stuff like “ST Audio DIP42” into google. After finding promising datasheets, I then verified their pinouts buy tracing the power and ground sources in the radio. Here is the cross reference of what I was able to find. I also found this interesting PDF which is a early 90’s listing for ST Micro parts. I was able to find the TDA7340S IC with it.
The IC that does the sound muxing, volume, and tone control is the TDA7340S and I figured this would be the best place to inject the Bluetooth audio signal.
Above is the block diagram. After the audio mux the signal travels to an external effects loop which consists of in series 1uF electrolytic capacitors. Then the audio signal travels into the volume and tone control parts. Perfect! If I inject the audio right before the capacitors I will retain the volume and tone control of the radio.
I thought about using the unused PHONE IN and then using a MCU to sniff the I2C buss and inject the right commands to switch it to that input but figured that would be more work then just injecting in the effects loop.
The next part is to make sure the signal from the Bluetooth adapter is compatible with what the TDA7340S is expecting. At max volume on my phone the Bluetooth adapter outputs a ~50mV DC offset signal with a ~1.7V to ~1.9V Pk-Pk. The signal in the effects loop was 4.65V DC offset signal with a 800mV Pk-Pk.
Since these signals are different I needed to adjust the signal of the Bluetooth adapter. I would need to apply a DC offset and then negative gain the signal from the Bluetooth signal. The opamp circuit below should do the trick. The feedback circuit is set to half gain and by applying half of VCC (via a voltage divider) to the other input of the opamp we can DC offset the signal.
I tested it by having my phone play a tone via a tone generator app called “Frequency Sound Generator”. Signal below.
Then to switch between the TDA7340S signal and the Bluetooth signal I found an analog switch IC made by Maxim, MAX4544CSA+. The opamp I decided to use was a AZ4558C. I decided to use it because it is a decent audio amp and fairly inexpensive. Lastly, since its stereo we need to double everything. Below is the schematic and layout I did in Eagle.
The files for the board can be found on my github. I uploaded the files to MacroFab and ordered the board.
I then soldered the board into the radio. I desoldered one leg of the the effects loop 1uF caps which are designators C112 and C113, then soldered hook up wire on the legs of the capacitors and into the hole in the PCB. The power for the Bluetooth module is pulled from the bottom of the radio. To switch the audio from the TDA7340S to the Bluetooth the input of the MAX4544CSA+ is pulled up. A switch on the dash will be used for this. See image below for how everything is hooked up.