Hi , i work with electronics and electronic repairs and know how to create a hex code from a .asm file and program a pic but do not know much about pic code designs . I would like to build a small pic chip project (i have only programed microchip devices) that cat enable or disable a relay coil to switch the AIRCON Condenser fan off at higher road speeds. The fans are wired to switch on and off every time the compressor is on but i would like to turn them off at road speeds 35Mph and above and enable the fans at below 35mph. The onle things i can tell you is this...

1 , Requires a input from speed signal from dash or gear box (i have no problem where to find the signal)
2 , Requires a output to drive a relay coil (i can add a output transisor to increase switching load if required)
3 , When speed signal is below 35mph relay must be off
4 , Road speed 35 mph or above relay switches on.
5 , some kind of a delay to prevent rapid switching of relay * 35mph


I would like any help or advice on what chip to use , and info on program design and how simple or complex this would be. The car for info only is my 1994 jaguar XJS V12 which i have converted to twin speed cooling fans which are controlled by a electronic temp control module and run at half speed when the aircon compressor is on. The car does not require cooling fans above 35mph due to the ram air cooling the engine and switching the ac fans off will save a load on the car battery and alternator.

Thanks for any help in advance.

 

That degree of modification is not something we can help with by our automotive guidelines:

Automotive Guidelines
Guidelines for automotive electronics help

1. Modifications to the ECU or engine sensors are not topics for discussion. Too many safety and legal issues come up. Air quality and safety trump performance.

2. Any homemade wiring modifications to signal or head lighting, or penetrations through the fiewall are not for discussion. The lighting function is to too critical for non-approved wiring and connectors. Many safety issues are involved. Preventing chafing in wires passing through driver-made holes is impossible to guarantee.

3. Add-on items that exist in the passenger spaces is generally okay. Exceptions are lights flashing to music and similar driver distractions. Assurances that the color organ will only get operated while sitting still is not credible.

Each OP should keep in mind the very public nature of these forums. While he may be able to install requested changes in a safe manner, there are others that may be tempted to do the same with no prior experience for guidance or proper tools for the work.

One further constraint to advice/help exists. We are international, but mostly have an audience here in the US. That means that we have to insist that aftermarket equipment must conform with US federal guidelines.

We have to choose a path between withholding all advice for fear of any possible harm, and simple telling anybody everything they wish, as they will only get the information on some other forum anyway. Neither extreme is sensible.
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