# Tachometer for AC50



## helluvaengineer96 (Oct 8, 2010)

Looking for input if anyone has got a Tach working with AC50 or its Curtis controller.

There are a two ways to get a Tach to work:
*1) Hook into cars existing tach.*
Need somehow to generate a pulse per every revolution and modify the existing Tach... For my Fiero this won't be very hard just pull the datasheet for the LM1819 and adjust one of the resistors to match 1 pulse per revolution.
*Generating the pulse:* I figured I could use a signal off the AC50 pigtail. But I can't find any documentation at all on the motor other than just it's dimensions. Looking at the Curtis docs it looks like there are two RPM signals, but that does not tell me much. Need to know p-p voltage, rise time, and pulse per revolution.
I'd prefer to use the pig tail but can always wire up something up the shaft that generates a pulse per rev. 


*CAM bus device*
When I started this I just assumed (whoops) that the Curtis put this information out on the CAM bus and that there would be an off the shelf Tach display. From what I can tell, this does not exist. Please let me know if I am wrong.


So I'm going to look at the AC50 pigtail RPM outputs with an O-scope and see what they look like and modify the Fiero's Tach.... unless someone knows of a cleaner solution.... ie CAM bus.


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## tomofreno (Mar 3, 2009)

> When I started this I just assumed (whoops) that the Curtis put this information out on the CAM bus and that there would be an off the shelf Tach display. From what I can tell, this does not exist. Please let me know if I am wrong.


 Motor rpm is displayed on the Curtis 840 gauge that comes with the AC50. The schematic in the manual shows the controller pin outs to the 840.


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## Thumper (Nov 24, 2010)

I struggled with the same problem on my AC50 project.
http://www.szott.com/zot2/zot2.html
I ended up using a Hall Effect Gear Tooth Sensor (DigiKey 480-2021-ND ~$25) to generate one pulse per revolution. I welded a "tooth" onto a standard 7/8" collar. Sensor bracket is a piece of 1/2X1/8 flat bar bent at 90 degrees and cut to provide a 2 mm gap between the sensor and the tooth. Sensor is fed with 12v and uses a 10k pullup resistor on the signal line.


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## helluvaengineer96 (Oct 8, 2010)

Thanks.. this helps. Now know that Curtis controller has RPM data in a memory location that can be accessed.

The 840 uses the serial bus not the CAM. Only wires going to 840 are the serial and power. 

My kit did come with the 840 so I at least have RPM digital read out to start with (which I did not know before).

Now to get it to an analog gauge or digital CAM ready device that has a Tach object.

Anyone have experience with CAM device that shows a display emulating a an analog gauge?


Thanks again.


tomofreno said:


> Motor rpm is displayed on the Curtis 840 gauge that comes with the AC50. The schematic in the manual shows the controller pin outs to the 840.


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## helluvaengineer96 (Oct 8, 2010)

Thumper,
That is a very professional set up you have there. Thanks for input. I'm ordering the pickup today.

Figure I can get the Fiero's analog gauge up and working pretty quickly with your setup. I'm still going to look for and integrated CAM solution, but I have a feeling this will take longer.

Thanks again for input.

BTW: just followed your link, great project car!



Thumper said:


> I struggled with the same problem on my AC50 project.
> http://www.szott.com/zot2/zot2.html
> I ended up using a Hall Effect Gear Tooth Sensor (DigiKey 480-2021-ND ~$25) to generate one pulse per revolution. I welded a "tooth" onto a standard 7/8" collar. Sensor bracket is a piece of 1/2X1/8 flat bar bent at 90 degrees and cut to provide a 2 mm gap between the sensor and the tooth. Sensor is fed with 12v and uses a 10k pullup resistor on the signal line.


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## Fiero_GT-EV (Jul 4, 2009)

Hi,
Can you tell me what size/type of hex cap screw you used to attach the sensor to the motor?
Thanks,
Martin



Thumper said:


> I struggled with the same problem on my AC50 project.
> http://www.szott.com/zot2/zot2.html
> I ended up using a Hall Effect Gear Tooth Sensor (DigiKey 480-2021-ND ~$25) to generate one pulse per revolution. I welded a "tooth" onto a standard 7/8" collar. Sensor bracket is a piece of 1/2X1/8 flat bar bent at 90 degrees and cut to provide a 2 mm gap between the sensor and the tooth. Sensor is fed with 12v and uses a 10k pullup resistor on the signal line.


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## bjfreeman (Dec 7, 2011)

helluvaengineer96 said:


> Looking for input if anyone has got a Tach working with AC50 or its Curtis controller.
> 
> There are a two ways to get a Tach to work:
> *1) Hook into cars existing tach.*
> ...


are you referring to CanBus?
I looked at a curtis 1230 which used the 840.
it had and encoder input
J2-1
J2-2
J2-4
J2-5
I saw` no CanBus connector

the do have two contorller they do have Canbus for 
Model 1310 canbus is J2
Model 1352 eXM pin 4&6

they use Class B for normal things like speed and Class C Can communications (canbus 2.0) for critical stuff.'
Their manuals cover the PDO used.


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## mizlplix (May 1, 2011)

OK, I wimped out and got a netgain sensor. it works with both a stock in-dash and aftermarket tach.








This set up is bullet proof and flexible as to the tachometer used.


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## mcbrems (Oct 28, 2011)

HPEV says that pin 2 of the 35 pin connector on the Curtis 1238-7601 is a general driver that they program to output a tach signal. If you will be using the original tach, I assume they will need to configure pin 2 output to match the point closing timing of the original gas engine. The table of pins for the controller is on page 13 of the Curtis PDF manual:

http://www.uqac.ca/~riceazar/1234_36_38_08july11_os11.pdf

As I understand, the original tach was triggered by the points, which in a Porsche 914 closed twice per revolution of the crank (all 4 cylinders firing per 2 crank revolutions). HPEVS also says that an opto-isolator (optocoupler) needs to be placed between the controller and the tach because both components are on entirely different electrical systems. They will be selling the modules and harness to connect it to the tach in about a month, they say.

Cheers
McB


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## MemphisPapa (Feb 16, 2012)

mcbrems said:


> They will be selling the modules and harness to connect it to the tach in about a month, they say.
> McB


I wonder how much this will be and maybe it is worth sticking with a separate sensor to keep the separation between the 12v system and the high voltage drive system.
Just a thought.
Thanks.
Memphis


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## frodus (Apr 12, 2008)

Bottom of the page:
http://hpevs.com/catalog-ac-50-26-28.htm

Shows how to connect an opto isolator to the 1238 controller, pin 2

Opto's aren't that expensive, so it shouldn't be that much, but you'd need to rent/buy a programmer to set it correctly for your tach.


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## ricklearned (Mar 3, 2012)

frodus said:


> Bottom of the page:
> http://hpevs.com/catalog-ac-50-26-28.htm
> 
> Opto's aren't that expensive, so it shouldn't be that much, but you'd need to rent/buy a programmer to set it correctly for your tach.


Just to clarify, the programmer is to program the Curtis to the pulses needed by the tachometer, correct?


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## frodus (Apr 12, 2008)

Yes, you have to set some parameters inside the 1238 to get the Tach working correctly. On cars, the tachometers are usually set to listen to pulses on a 4,6,8 cylinder vehicle so they're all different.


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## ricklearned (Mar 3, 2012)

mcbrems said:


> ...... They will be selling the modules and harness to connect it to the tach in about a month, they say.
> 
> Cheers
> McB


That was in June. Any updates?


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## frodus (Apr 12, 2008)

I'm checking now. I've been out of town for a bit and forgot to check in. Will post an update.


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## frodus (Apr 12, 2008)

I got pricing and availability so they're available to order through me. Single channel opto-isolators are $50 plus shipping. I'll be updating my website today to include these optional devices.


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## albo2 (Oct 4, 2011)

frodus said:


> Bottom of the page:
> http://hpevs.com/catalog-ac-50-26-28.htm
> 
> Shows how to connect an opto isolator to the 1238 controller, pin 2
> ...



Thanks for the info, it looks like it is set up by default for a 4 cyl, which I would imagine all AC50 conversions would be, I have the tach running on the serial data stream but will give this a go doesn't sound too difficult.


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