I run my car off a eprom emulator and recently found out that because of the older design of the vehicle electronics; the emulator is always on and killing my battery. 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. My only option is to now kill all 28 connections (yes, I could just pop the hood and disconnect it every time I drive. But what fun is that.)

So far I have a circurt that will be triggered by an RFID key. When I toggle it it should trigger a relay on untill I toggle it again (I'm using the design Single MOSFET Relay Toggle Circuit about half way down this page http://ourworld.compuserve.com/homepages/Bill_Bowden/page9.htm#toggle.gif, the only difference is that the relay I'm triggering has a higher resistance of 360 instead of 120. If anyone thinks that would be an issue let me know). That was going to connect pin 28 ground; now I'm not sure where to go since I have to connect all 28 pins. I figure I could wire that relay connection to vehicle power and use it to trigger 14 DPST (high restance) relays in parallel, but honestly that seems like a real waste of power and space. Is there something smaller or that uses less power someone can suggest. I'm pretty new at this so I'm sorry if this is a real easy problem and I just don't know the answer. Thanks.

 

Well I think I may have a solution for power consumption, but it still seems ugly to me. I have the RFID toggeling a relay which acts like a momentary switch for the circuit I posted earlier. That circuit switches on and off a 4PDT relay that keeps the circuit active (until momentary switched again), provides an aux switched power, and also acts to reverse polarity on 14 DPDT single coil latching relays connected in parallel with 14 50v 33uF bi-directional caps. My theroy is that when activated (not inital power, but in general) the polarity change will discharge the caps and acutate the relays then the caps will refill and stop draining power until actuated again when it will move the other way. Below is a pic of my schematic (some of the 14 relay & cap combos are cut off). If anyone has a suggestion to better the design please let me know. I would love to save some space by reducing the # of relays (I though about higher pole# relays, but they are too expensive) and if anyone has a simpler idea to reverse the polarity on the latching relays I would like to know it. Thank you

 

Well can anyone see any glaring errors i've made? I really want this to at least work if I flip the bill for it.

 

Well I ended up using 4 bus switches which drasticaly reduced the cost and size of this board. That said I've found that the extra resistance the board creates is causing too much signal loss; so I want to add a buffer line-driver to the design (I believe). I know I've seen a design that uses 74HC573a to drive the data lines, but I can't find a schematic for it (and I don't know how to calculate the value for the pull up resistor). Does anyone have one or a link to one so I can add it into the board? Below is a semi-current pic of my board (I removed the 100uf cap on the lm7805 since I didn't add another on the other side, but the rest is the same). Thanks.

 

Does a 74AC245 bus transceiver drive the lines as well as allow asyncronious data flow?

 

Ok, here is my redesign. I know the momentary 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.

 

Will someone at least please tell me if I'm using the buffers properly?

 

Is everything I'm posting nonsense? I really need some advice so I have some idea that I'm not just wasting time and money putting this together.

 

Bump for the day.