Controlling the Instrument Cluster's Display

Right now, my hands assemble the boards! Only for prototypes of course. I haven't decided on a fab/assembly house yet, probably will try to find one stateside. Since I bought all my components I'll have to ship them to the fab house, so would be nice if it's not in China (though will be more expensive).

I2C pullups will be on the daughterboard, since it could use any voltage between 2V-5V. Decoupling caps like 0.1uF would also be on the daughterboard. It would be easy to add one though, I probably will.

The 5V capacitance is probably overkill. The joystick is on the end of a ~3ft cable, not super long but not short. The buzzer plus LEDs could draw up to 250mA instantaneously so I wanted a decent amount of capacitance.

No net problems, probably just something weird with the PDF export.

It is a tiny buzzer! 4x4mm. I found it a while back for a watch project I did. Not super loud, I'll have to see how it sounds in a noisy car. Nothing else would fit, though. I could potentially put a larger buzzer on the mainboard instead of the tiny one on the controller.

Two problems using U2:9 to drive the buzzer - it requires pretty high current (150mA instantaneous), so I'd have to raise the current limit for all LED channels just to drive that one channel. Also, changing the buzzer frequency would change the PWM frequency for the LEDs, which could cause visible flickering if I did really low-frequency beeps. Though anything above 100Hz or so you'd only see flicker when you move your eyes, but I find that effect annoying. Definitely a more minor point, the current limit is the real issue.

I definitely agree with through-hole connectors and other mechanical parts (like the encoder). I always, always choose them wherever possible. Unfortunately, not possible in this case. Not shown in the pictures is the 3D-printed clip that screws on to the back of the board, this retains the whole assembly in the knockout panel hole. I'm going to add a loop that the cable will be zip-tied to, so there should be no strain on the connector. The user should never have to unplug this cable anyway.
The pads are about as large as they can get. I wanted to flip the connector 180 so I could make them bigger, but there are features in the knockout panel hole that I need to avoid, so it had to be in this orientation.
This connector also uses a clip for retention rather than detents, so much less force when removing it.

Thank you for the feedback!

I have a conundrum, and I'd like anybody who's interested in buying Pegasus to weigh in on it.

I've always wanted Pegasus to be a drop-in kit, with no soldering required. However, I would be able to greatly reduce cost, complexity, and size of the power supply components for Pegasus if I require soldering two wires to the cluster PCB. This would also reduce the size of the OBDII plug by a lot. For 01-06 cars, this is more significant since the OBDII port is by the driver. If you had Pegasus and OBDIIC&C plugged in, it might get to the point of brushing against your leg if the Pegasus plug is too large.

The soldering is easy enough that I believe anybody who's used a soldering iron before shouldn't have much trouble doing it. You'll need to solder to this cluster test pad, plus a second similarly-sized one somewhere else that I haven't decided on yet. There's also a through-hole capacitor on the board that could be an alternative easy soldering point.



Here's why I want to require this soldering.
The cluster LCD connects to the cluster PCB with a flat flex cable. When you install Pegasus, you unplug this cable and plug it into Pegasus, and plug Pegasus into the cluster board instead.
This cable provides 5V, ground, and the display signals to Pegasus. The prototypes ran directly off this 5V provided by the cluster. I can't do this on the new one because I will be using more power than the cluster regulator can handle, and I want to affect the cluster operation as little as possible. Instead, Pegasus runs off the 12V from the OBDII port and regulates it to 5V.

This presents an electrical problem. Pegasus is connected to the ground at the cluster, but also to the ground at the OBDII port. The cluster and OBDII port are also grounded elsewhere in the car's electrical system. This creates what's called a ground loop, which acts like an antenna and picks up electrical interference. It could also cause unintended current to flow through sensitive areas of the cluster. This could potentially negatively affect Pegasus and the cluster. I could just try it and see how things look, but it's really not the right way to do things and I wouldn't feel comfortable shipping it to people.

To keep Pegasus plug-and-play, I need to design an isolated power supply that would sit in the OBDII plug. There's not enough space in the cluster to put it on the Pegasus mainboard.
There are some downsides to doing this:

• Need to add large protection components to the regulator input (car electrical environment is not friendly)
• Isolated regulators are expensive and hard to design
• The voltage output from a regulator like that isn't very stable, so I still need a second regulator on the Pegasus board
• The transformer is physically large and makes the OBDII plug bigger

There are some upsides to soldering to the cluster PCB and getting power from it:

• Cluster PCB already has those large protection components since it needs to protect itself (reduces size and cost of protection needed on Pegasus board)
• Secondary regulator still needed on Pegasus board, but is small and cheap
• OBDII plug stays small

What do you think? Does the soldering sound simple enough that it wouldn't affect your choice to buy Pegasus? Or is it a dealbreaker for you?

I am "ok" w/ soldering - will this work?

Personally, a harness sounds safer to me than surface mount soldering for the masses.

I got the controller PCBs a few days ago, and had time to assemble the 4 of them today. Tomorrow I will power them on and, assuming the microcontroller works properly, write some code to test everything else to make sure it also works!