COP (toyotas) and MS standalone tach issue - Page 4 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 09-04-2007, 05:58 PM   #61
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whoa, tach only needs 1V?! Probably need a 317 to regulate voltage instead of just a resistor then.
Its not so much that the Tach only needs 1v. It has power/gnd going to it from the in cabin harness.

Its that the tach outputs from the COPs need that 1v signal that would normally come from the ECU.

So as talked about,
Standalone MS = 1k from 12v to tach wires (which as Lazzer mentioned, can be done at the ecu plugs easily... so you can still merge the 2 wires together for possibly other configurations)
MS with OEM Ecu = just jumper the 2 wires together.
OEM Ecu = just jumper the 2 wires together.
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Old 09-04-2007, 06:31 PM   #62
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aiight, thanks for clearing that up.

i figured as much, i started wiring mine and didnt want to have to go back in later.
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Old 09-04-2007, 07:03 PM   #63
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Dave I get it, my objection was with the high voltage feed instead of 1V.
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Old 09-05-2007, 02:16 AM   #64
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Dave I get it, my objection was with the high voltage feed instead of 1V.
"High voltage" being 12v thru the resistor instead of a regulated 1v? I don't think the voltage really needs to be regulated. It's just something the tach needs to compair a 0v tach pulse against. I'm suprised Mazda didn't do all this in the tach itself. It seems overly complicated just for a tach signal. 1k limits the current at 12ma (.012a). Not enough to fry anything. If you -really- want to lower it use a resistor divider (series network) of 1k to v+ and 10k to ground. The center will give you 1.1v.

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Old 09-05-2007, 02:27 AM   #65
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thats funny, I was telling split to do a voltage divider a couple days ago when this was first mentioned.
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Old 09-05-2007, 08:36 AM   #66
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Yeah "high" meaning 12 instead of 1.
I'm not convinced it needs a regulator either, but it's just as simple to do.
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