Digital Input question

[Pete_89t2]

Will the DI1 input on a Fury G4+ accept a 0-5VDC TTL type square wave input? If so, would I need to apply the pull up option?

Some background - I'm currently using a direct connection my car's vehicle speed sensor (VSS) on DI1; car is a series 6 FD RX7. The VSS is a 2 wire VR type sensor that outputs a sine wave at 8 pulses per revolution of the sensor. So basically the frequency of the VSS varies as speed increases; I have it calibrated & setup in my G4+ to measure driven wheel speed which works just fine for use with the G4+, but I've discovered that doing so causes the OEM dash speedometer to read a few % higher than actual road speed when calibrated against GPS or via the time/mile marker measurement method.

After reviewing the FD's shop manuals, I found that there is another possibly better way to obtain my vehicle/driven wheel speed signal, assuming it's compatible with the G4+. The FD's OEM instrument cluster outputs a 4 pulse per VSS rotation square wave signal that it normally would send to the OEM ECU and OEM cruise control unit. According the the shop manual, this signal reads on a DC voltmeter approx. 5VDC when the car is keyed on/not in motion, and approximately 2.5VDC  when it is in motion, which implies to me that it's a TTL logic output (0V/5V). So the thought is if I tapped this signal for DI1 instead of doing the existing direct VSS connection, it might eliminate the speedo error I'm seeing on the OEM cluster speedo.

[koracing]

That should work I think as the DI's typical trigger threshold is around 1v (must pass above and below 1v for high/low signal for it to register the trigger edges).  Enabling the pullup on square wave (hall sensor type signal) can lower the low voltage part of the signal making it drop below the 1v threshold more reliably as I understand it.  As it's being driven from the OEM dash it should be pretty easy to test with and without the pullup enabled, however.

[Adamw]

4 hours ago, Pete_89t2 said:

but I've discovered that doing so causes the OEM dash speedometer to read a few % higher than actual road speed when calibrated against GPS or via the time/mile marker measurement method.

I cant see how having the Link ECU connected in parallel would change the frequency that the speedo receives.  It is pretty normal for OEM speedos to read higher than reality, quite often more like 10%.  

[Pete_89t2]

8 hours ago, koracing said:

That should work I think as the DI's typical trigger threshold is around 1v (must pass above and below 1v for high/low signal for it to register the trigger edges).  Enabling the pullup on square wave (hall sensor type signal) can lower the low voltage part of the signal making it drop below the 1v threshold more reliably as I understand it.  As it's being driven from the OEM dash it should be pretty easy to test with and without the pullup enabled, however.

That's good news, thanks!

 

5 hours ago, Adamw said:

I cant see how having the Link ECU connected in parallel would change the frequency that the speedo receives.  It is pretty normal for OEM speedos to read higher than reality, quite often more like 10%.  

It wouldn't change the frequency of the VSS sensor signal, but having a 2nd load (Link ECU input) wired in parallel would change the AC impedance some, which may impact the accuracy of the OEM speedo.