Mechanical speedometer drive solution

[Second Series]

I found that the laptop does not recognize a usb cable with no power(red wire cut). I was able to start the truck and then connect the laptop to the Arduino. Troubleshooting the erratic needle movement I added a line in the code to monitor the input frequency. With the truck idling and stationary there should be no input. I was seeing a signal. I temporarily shielded the box with aluminum foil and the input wire with copper tape, but that didn’t fix it. I disconnected the input wire, and then the power wire. Of course with the power wire disconnected there was no needle movement, but I continued to see signal at the input with both wires disconnected. The input signal goes through a 5v regulator, a jumper, and into the Arduino. I removed the jumper and no longer saw a signal at the input.
I designed the circuit with minimal parts. I now added a capacitor to the input signal to get rid of this unwanted noise. At first I attached a 1uF cap. That completely eliminated the erratic needle movement, but the speedometer would go no higher than about 35MPH. I then tried a .1uF cap. That allows the speedometer to go over 60MPH, smooth movement. There is some delayed settling when coming to a stop, I’ll keep tweaking the code.
I got some ideas from nsocwx’s build and found an opto-isolator that could work instead of the 5v regulator and capacitor.
I ordered some more parts, and am creating a BOM, list of parts. I’ll document everything as I build a second unit. I found a motor from a robot website that could work, but still waiting on delivery.