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.
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.
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.
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.
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:
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.
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
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.
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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