Info on using stock tach...

Post by **rbsileighty** » Mon Aug 22, 2005 5:38 am

Has anyone used the pull up resistor in order to use the stock tach? I was searching around today and found this info from a VL forum:

Quote »The RB20 tacho uses a 0-5V square wave signal. The ECU only appears to switch pin 7 between open and ground, so i'm assuming the tacho provides it's own 5V connection to pin 7 through some internal electrics.[/quote]So if anyone has tried the pull up resistor... looks like that might work since another post in the same thread recommended the pullup resistor as well (resistor that is connected between a 12V source and the tach signal wire).

Post by **Wulfgang** » Mon Aug 22, 2005 7:57 am

Yep, that is exactly what I found. The ECU appears to just invert the #1 coil signal with a low side driver. For the S14, the tach sources 12 V, so you get 12 V pulses instead of the 5V in that quote. No pull-up resistor is needed.

For the S13, I do not know if the resistor is needed. GTR_Shop said it was necessary. Certainly, with 10k you can't go wrong. If the tach does have internal pull-up, then the added 10k won't break anything, and the tach should still function correctly.

Post by **240240** » Mon Aug 22, 2005 9:33 am

So, lemme make sure im getting this right---there is a resistor between the tach pin (Pin 7) and the 12v battery. Take this resistor out and the 240sx tach will work correctly?Currently im using SAFR for my tach and dont like it because its digital

Thanks

Post by **rbsileighty** » Mon Aug 22, 2005 10:21 am

No, there is no resistor there and you have to add one. I got a pack of them from Radio Shack for less than $1. I am not at the car for another month or so... no chance to try it out so far.

So your tach reads correctly with the RB signal wire connected directly Wulfgang?

Post by **Wulfgang** » Mon Aug 22, 2005 12:08 pm

Yes. No resistor is needed on the S14 (but it of course must still be calibrated using the potentiometer on the back).

Post by **rbsileighty** » Mon Aug 22, 2005 2:48 pm

Huh... so after cal with the pot on the back you can get accurate readings through the rev band... interesting. Kind of strange since it's a four cyl tach reading a 6 cyl signal... what have you measured it against? I do believe you... a RB guru on the aussie boards told me that using a CA18 tach would work since the CAS is the same... again... interesting.

Post by **GTR Shop** » Mon Sep 12, 2005 8:23 pm

Bolt a C33 tacho in and be done with it You can use a pullup resistorand add another resistor inline witht he pot to adjust but it makes the tacho read slower.

Info on using stock tach...

Info on using stock tach...

Re: (Wulfgang)

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