This project makes a Bluetooth adapter for the G750 foldable keyboard. This keyboard was meant to use with vintage PDAs (Windows CE, Palm, Clie etc.). It was sold under various brands (HP, Compaq, Dell, Treo etc.) and has multiple model numbers (G750, G7L0, G7L1, etc.). But as long as they have the same look, this adapter should work for them.
There is one exception: G700 for Toshiba, it uses USB protocol instead of serial, so it can not be supported. (There is also a G700 for Palm and Sony Clie, maybe that can be supported, but I haven't tested it yet.)
Note that there are two variants of the electrical characteristics: G750 uses inverted-TTL for its RX line, while G7L0, G7L1 uses TTL level. Some keyboards also have one or two extra keys depending on the layout and the PDA's OS. See the protocol analysis and keycodes for details. Therefore, the hardware wiring and the firmware are slightly different for different models.
The G750 keyboard uses an distinctive folding mechanism that slides out to both sides, while the middle piece raises up to the same level. A connector is prop’ed up to provide connectivity to the PDA. This project achieved Bluetooth functionality by replacing that connector module with a custom designed Bluetooth module.
| Brand | Model | Supported | logic level |
|---|---|---|---|
| HP | G750 | Yes | inverted TTL |
| Compaq | 249711-001 | Yes | inverted TTL |
| ViewSonic | PPC-KYB-001 | Yes | inverted TTL |
| Dell | G7L0 or G7L1 | Yes | TTL |
| Treo | G740 | Yes | TTL |
| Belkin | G700 for Toshiba | No | USB protocol |
| Belkin | G700 for Palm/Clie | ? | Not tested |
The keyboard itself can be found on eBay for around $20. You can search using the keywords "G750", "249711-001", "G7L0" or "G7L1" + "Keyboard". G740 for Treo has a weird key layout, but if you are willing to swap keycaps, it's also a viable choice.
If you want the adapter, I've made some for sale at Tindie. https://www.tindie.com/products/36279/
Protocol analysis and keycodes
Tutorial for making the adapter
Tutorial for installing the adapter into the keyboard
These are in a separate repo, the PCB design is shared with the Palm Portable Keyboard Bluetooth mod. The PCB uses a WCH CH582F chip, a RISC-V based Bluetooth controller. It is low cost, power efficient and easy enough to use, which is why I chose it.
It is a known issue that these keyboard's spacebar can't reliably register. But there is a simple fix for that.
