Doubling the pusle count

[malc-c]

Darrel,

I've made a small PCB based on your schematic above, and sent it to my mate with the car to try. The PIC was programmed with your version 3 code.

I've received a mail from him asking the following

Do you think I should leave the two "control" wires open for starters and only mess with them if it doesn't work right stright off???

The two control wires he mentions are two wires for the idle and invert options. I suggested he leaves these un-connected first off and see if there is a change in the speedo reading, but wondered if you could clarify (in laymans terms for both me and Brian) how these options affect the processing of the signal from the sensor (or how it should affact the output)

[mister_e]

As long as the internal pull-up are good enough to reject the possible incoming noise, it won't cause any problem... but i'm not a internal-pull-up oriented guy for a final product... but once again it's me.

[malc-c]

I thought about adding a couple of external pull up resistors, but didn't know ( I know, should of asked ) if taking them high would of caused problems.. Its not a problem as they can be added at the switch

[Darrel Taylor]

I think if there are antenna's (a.k.a. long wires) hooked up to the option pins, the internal pull-ups may not be good enough. Small jumpers or dip switches should be ok though. No problem adding external pull-ups if desired. Or you can tie them directly to VDD or VSS.

With the IdleState pin left open, the program will assume the input idles HIGH, with negative going pulses, which is the opposite of the 0-12-0 polaraity described before. So I'd start with that pin grounded.

The Invert input should be left open, without any wires, since that circuit uses the NPN transistor that inverts the output. It was just an option available for anyone else that might pick up the code from the forum. The output follows the same polarity as the input Idlestate, so there shouldn't be a need to change it with that circuit.

When you programmed the chip, did you uncomment the ANSEL line?
I was using a 12F629, but I think you're using a 675.
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[malc-c]

Thanks for the feedback.

I did see you note on the use of the chip, and missed it completely when I programed the ver3 of the code ! Bu99er !!!

With the ansel line remmed out and using a 12F675 - how would that effect the way the unit performed... (Brian - if you are reading this I'll send a new PIC to you if I screwed up !!)

[Darrel Taylor]

With the ansel line remmed out and using a 12F675 - how would that effect the way the unit performed

Without it, there won't be a performance.
The digital Input latches are disabled while in analog mode. So it can't see the pulses, or the options.

Sorry, I should have left it un-commented.

[malc-c]

[sware] beep beep beeeeeP [/sware]

I thought as much... I'll re-code and send him a replacement PIC

Next time I'll wear my glasses !!