Build a N8VEM computer
This is a modified version of the standard N8VEM with several enhancements including a keyboard, 4 RS232 ports, battery backed ramdisk, output to a VGA display and an onboard switching power supply.
Step 1
Get a board from here and obtain a parts list by emailing Or make your own boards (please email for the Eagle source files). Start by adding some sockets. High resolution photo of the board is here (for part placement). Screen capture of the Eagle board file is here. Complete Eagle file package is here.
Step 2
Add all the sockets and then place a piece of flat board on top of the sockets and flip the whole thing over. Then start soldering the sockets in place.
Step 3
All the sockets have been soldered in place. There is one wire link to add which fixes a bug that left half the chips with no power supply! It is a single wire link that can be soldered on the back of the board. ERRATA Photo is here
Step 4
Now add the bypass capacitors and the three resistor networks. These are all the same height as the sockets so you can use the same technique of putting a board on top and flipping it over.
Step 5
Add some more components. Keyboard socket, 2 RS232 sockets, DC power socket, capacitors for the power supply and RS232, socket for the battery backup, leds, reset button and capacitor and a 16 way socket for the LCD display.
Step 6
Now add some chips. The two oscillator clock modules have been added. Other chips are ready to go in. Shown also are a IC pin straightener and a IC remover - both invaluable tools are available from futurelec
Step 7
Program an eprom. This is a Willem eprom programmer available from many sources eg ebay. Insert the chip and download a file that contains the operating system and some useful files. You may need an eprom eraser if you do lots of eprom programming. The eprom image is available here Alternatively, send an email and we can send one pre-programmed.
Step 8
The completed board with all the chips inserted. Total time was about 45 minutes. You can download programs via a terminal program on a PC, or use it with a standalone vga screen and a Pocketerm board.
Schematic is available here
Parts list is here
More details including files and more photos are on the N8VEM site.
Step 9 - box them up.
These are four router boxes. There is the socket for the keyboard at the back and a RS232 connection to external boards. An antenna is visible on the right hand side, and this is used for file and data transfers to other boards. Radio modules are from Yishi.
Step 10 Inside the box
Inside this box is a N8VEM board, a Propeller Pocketerm for talking to a VGA display, the LCD display and the Yishi wireless module. There are many wireless modules around, but Yishi ones have a large buffer (256 bytes) and a buffer is needed to run xmodem for file transfers.
Step 11 - write some code
The router software handles packet capture, store and forwarding. It is written in sbasic for the Kaypro CP/M computer. Attached is a screenshot.
Source code is available here Sbasic instruction manual is here and the disk image and software is available for the Altair simh CP/M simulation here (scroll down to Languages/Basic). For those that already have CP/M and just want the programs, a zip of the sbasic package is available here. The vb.net Integrated Development Environment is available for download here. The .net program is available for download for free from Microsoft here.
Step 12 - Listen to the network
This is the mesh listening to one board. One board (iota) is generating messages. Other router boards are listening and occasionally send their messages too to say they are active. Data packets have a source, destination, message type and 8 data bytes. This screenshot is from the Propeller Pocketerm driving a vga monitor directly (no PC needed). Text colour, baudrate etc can be changed on the fly using function keys.
Step 13 - Hardwiring a base station
From the top down, vga monitor (used for both PC and for N8VEM), keyboard for N8VEM, N8VEM in a 19 inch rack case with display and switches and two voltmeters to display tank levels, keyboard for PC, PC. This base station contains several picaxe boards that detect packets to display tank levels on a 5V analog voltmeter. The base station also has a N8VEM that acts as a router. It contains an RS232 router board which connects the picaxe boards and N8VEM board and a connection to the radio module.
Step 14 - Wire up an antenna
The key to long range data communications is to get the antenna up high. The shed is 2.4 metres high and there is another 1.5 metres on the pole. The small black box contains the Yishi RF module. There is a 4 wire connection - Gnd, 5V, Rx and Tx. The box also contains a 4700uF capacitor across the 5V supply. Range has been tested to 1km through trees and over a hill. The mesh can be tested with a little program called meshping.
