Andy wrote:
Hiya,
As per my earlier posting I've now designed and built a universal E2/E3 interface board that should convert to/from legal RS232 levels. A jumper is used to select E2 or E3 mode. I've also produced a circuit diagram from my prototype and put this here:
http://www.cambridgewargames.org.uk/members/andy/emailer/
I would welcome any feedback on the design and would also appreciate people sanity check I've not put any stupid mistakes in the circuit diagram when copying from my stipboard prototype.
The 1K resistors are not quite adequate protection on the input of IC1A. A static spark could easily generate 2Kv, or a 2A pulse. This will probably not kill the 4070 the first time.
Four diodes, one each between the tip/ring connections, and VCC/ground would be a good idea. 1Nn4148 or similar would be fine.