USB Caliper HID

Ergonomics .....At this point, I will be locating the function switches (and possibly the Trinket) onto the caliper body.

Incomplete, and a little buggy, but it reads caliper packet , and can output via USB.

Umm......at some point, I reread the guidelines for the Trinket contest -- "must be battery operated".

Anyway, long story..short, the HID module will operate from a battery (if you bother to plug one in), but it will operate off of the USB bus just file.

You can ignore any reference of battery stuff in the write-up -- unless you're a stickler for details.

I've had a really unsuccessful time in trying to get the USB HID to work on the Trinket Pro. From what I had seen, and read on the web, it should not have an easy task.

The problem that I encountered was that the Trinket bootloader(USBTiny) would start up, and it would be enumerated by the host system correctly. But, when the bootloader passed control to my sketch, the host would always failed to enumerate the Trinket as a Keyboard HID -- it would remain a USBTiny.

I spent several frustrating days trying to get it going. Out of frustration, I ended up modifying the Trinket.

It's a simple change. I added GPIO control of the USB pull-up resistor. I now works consistently.

The change which I made is to allow the sketch to pull the USB data low/high which causes the USB host to re-enumerate.

There might be a non-hardware solution, but for now, I am going to leave it alone. The current mod uses a diode, but just a wire may be sufficient.

The calipers that were chosen are commonly available, and inexpensive -- under $15 when on sale. They are available at Harbor Freight(US), and Canadian Tire(Canada). They are OEM'ed to large retail distributors, and will look slightly different. So far, from what I've seen, the shape of the electronics housing and the color of the buttons remains consistent.

There are a few people out there who have already interfaced to similar calipers. Some info is available on the web regairdng the different interfaces available.

I needed to be sure about the caliper that I purchase, so, I undertook to have a looksy. Here's what I found;

At first, I thought that it might be outputting in BCD, but that was not the case. Maybe it uses a 4-bit processor?