quantumkid
New Member
I run my car off a eprom emulator and found out that because of the older design of my vehicle electronics, the emulator is always on and killing my battery. Was originally going to I designed a board that killed ground at "pin 28" to shut if off, but after talking to the emulator developer he recomends I don't do that because the emulator my try to use an address pin for ground. So my only option is to kill all 28 connections (yes, I could just pop the hood and disconnect it every time I drive. But what fun is that).
I designed and built a board that used 4 8bit bus switches (with ~4ohms of resistance per channel) to cut all the connections, but it seems that there is too much resistance and though the emulator will power on it does not communicate.
Here is my redesgn of the board.
**broken link removed**
I know the momentary switched power works properly (the entire left side of the circuit), so i'm not worried about that. I took out the bus switches and replaced them with CY74FCT541ATPC buffer drivers (data sheet) and one more 4PDT relay for 4 of the non data pins.
Since it would be a huge mess with the nets showing I'll just type out how they are connectd. Vcc, Vpp, OE, and CE all connect through the added 4PDT relay. I did this because I not sure how the buffers handle the ostrich power running though them. OE and CE I moved because they don't carry any data and only need voltage (I believe). If anyone thinks I can get away with connecting those four through a buffer let me know because it is cheaper. The address lines (A0-A14) connect from the ECU to the input side of the buffer then output to the Ostrich while all the Output lines (O0-O7) connect from the ostrich to the input side of a buffer then output to the ECU. I connect both the ECU chip ground and the Ostrich ground to ground on the board (If you think that board ground isn't a good idea; I can move it to a relay if I give up the aux switched power). When powered "off" the buffers gates are held at Vhi which should create HiZ on the lines and keep the ostrich from drawing any power from them. I can post a pin out of the headers telling which pin on a 27C256 they represent if someone wants it.
Since I'm rather new at this I would really like to know if I'm using the buffers correctly? Also If anyone sees another issue (Like; I can/should use a buffer for OE and CE or a need to connect ECU chip ground to the emulator ground instead of a common ground) please let me know. Thank you.
I designed and built a board that used 4 8bit bus switches (with ~4ohms of resistance per channel) to cut all the connections, but it seems that there is too much resistance and though the emulator will power on it does not communicate.
Here is my redesgn of the board.
**broken link removed**
I know the momentary switched power works properly (the entire left side of the circuit), so i'm not worried about that. I took out the bus switches and replaced them with CY74FCT541ATPC buffer drivers (data sheet) and one more 4PDT relay for 4 of the non data pins.
Since it would be a huge mess with the nets showing I'll just type out how they are connectd. Vcc, Vpp, OE, and CE all connect through the added 4PDT relay. I did this because I not sure how the buffers handle the ostrich power running though them. OE and CE I moved because they don't carry any data and only need voltage (I believe). If anyone thinks I can get away with connecting those four through a buffer let me know because it is cheaper. The address lines (A0-A14) connect from the ECU to the input side of the buffer then output to the Ostrich while all the Output lines (O0-O7) connect from the ostrich to the input side of a buffer then output to the ECU. I connect both the ECU chip ground and the Ostrich ground to ground on the board (If you think that board ground isn't a good idea; I can move it to a relay if I give up the aux switched power). When powered "off" the buffers gates are held at Vhi which should create HiZ on the lines and keep the ostrich from drawing any power from them. I can post a pin out of the headers telling which pin on a 27C256 they represent if someone wants it.
Since I'm rather new at this I would really like to know if I'm using the buffers correctly? Also If anyone sees another issue (Like; I can/should use a buffer for OE and CE or a need to connect ECU chip ground to the emulator ground instead of a common ground) please let me know. Thank you.