I decided that SMS and chat apps are far too convenient, so I made my own texting system with some old Pocket PCs and 2-way radios! This lets me send and receive messages and files wirelessly. No cell phone, Wifi, or network required! This wasn't exactly an easy project, as it took a few days and a few trips to the surplus store to get it all working. However, it was a lot cheaper than doing the same thing with a microcontroller or mesh network! The whole project cost about $50, including the old radios, old PDAs, and random junk that went into it.
The PDAs I'm using are Motorola MC55A PocketPCs running Windows CE. I found several NBT radio modems at Ax-Man surplus (www.ax-man.com/). I combined those with '90s-era color dot radios (Business Band / MURS). The Pocket PC connects to the modem with a serial port cradle and null modem adapter. The modem connects to the radio through the speaker and mic jacks.
Software I used was Terminal CE (www.venea.net/web/terminal_ce) and MobileVT (www.mobyware.org/windows-mobi...)
I found that one terminal app worked better for sending and one was better for receiving. I used 300 baud, N/8/1, and I have all the flow control (CTS / DTR) turned off.
Range with the business band radio is OK but not great (a block or two in the city, or about a mile in open country). The external antenna on the backpack version might have longer range.
The modems are a Bell 202 style, converting serial data into audio tones with AFSK encoding. They can theoretically handle up to 1200 baud speeds, but I've kept everything at 300 baud to make it simpler and more reliable.
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11 июн 2024
