Question: Question regarding DDS signal generator

[THEFERMANATOR]

I'm looking at doing some gauge cluster work on my BURB, and to do what I'm looking to do I need some sort of generator to create a switched to ground signal to mimick the speedometer signal from the ECM. It would also be nice to find one that could also do the opposite and switch to 12 volts positive for calibrating tachometers. I have found I can use a battery charger to do gas tachs, but would like something capable of doing more pulses per minute so I can calibrate an alternator driven tach as mine is run off the alternator, and sees about 7 times as many pulses per minute as a V8 does. I've been looking on EBAY, and have come across some DDS signal generators that look like they would work, but was trying to find comformation from somebody with more knowledge of circuitry as to wether or not one of these would work. I'm not wanting to spend much money on it as I won't be using it alot, hence why I'm looking for cheap stuff on EBAY. Any help is MUCH appreciated.

 

[turbo_bu]

You could try and make one using a 555 timer chip. Google square wave function generator and you should find some stuff. Basic circuit that you can put in a variable resistor to regulate the output frequency. Might also need a voltage divider on the output to regulate the desired square wave voltage.

 

[THEFERMANATOR]

I rolled the dice and ordered a 10MHZ one from ebay. I'm doing some custom cluster work for my BURB, and need something calibrated. I was able to find that I needed 15 volts to drive the tach, and that the speedo gets grounded. So it looks like I can install a 1K ohm resistor to ground for the speedo, then the signal generator will work for it as well. Tried it with an old school battery charger which works for the tach, but unfortunately it drives the tach at 108MPH on a 100MPH tach, so it just doesn't have the needed signal for doing the speedo. I'll update later once I get the signal generator and figure out how to make it work. Probably would have been cheaper just to have paid a shop to have done my cluster, but I like doing stuff myself, and I may later on get into doing custom cluster owrk on the old style air core gaiges. Shops were wanting $40-60 just to redampen one gauge, and it doesn't cost but maybe $1-2 worth of silicone oil to do a whole cluster once you get all the different weights you need.

 

[THEFERMANATOR]

This what I ended up with. Works great, and has allowed me to accurately check my tach and speedo, and will also allow me to go to a custom gauge face and recalibrate the tach and speedo for it. I'm gearing up to do work on pre databus triggerred gauge clusters, should be an interesting venture. Still have a few more pieces to get to finalize all of my test stuff.

http://www.ebay.com/itm/161856560812?ru=http%3A%2F%2Fwww.ebay.com%2Fsch%2Fi.html%3F_from%3DR40%26_sacat%3D0%26_nkw%3D161856560812%26_rdc%3D1

 

[duratothemax]

This what I ended up with. Works great, and has allowed me to accurately check my tach and speedo, and will also allow me to go to a custom gauge face and recalibrate the tach and speedo for it. I'm gearing up to do work on pre databus triggerred gauge clusters, should be an interesting venture. Still have a few more pieces to get to finalize all of my test stuff.

http://www.ebay.com/itm/161856560812?ru=http%3A%2F%2Fwww.ebay.com%2Fsch%2Fi.html%3F_from%3DR40%26_sacat%3D0%26_nkw%3D161856560812%26_rdc%3D1

Looks like that one only does 10v peak to peak though? Didnt you need one that can do at least running battery voltage? 13-14?

 

[THEFERMANATOR]

Looks like that one only does 10v peak to peak though? Didnt you need one that can do at least running battery voltage? 13-14?

It does up to 20. The ad was vague, but one of the pics show 20V on the display. The manufacturer confirmed it. I found that the diesel tach which is alternator driven needs 6-8 volts to work, but will work on up to 15 before it cuts out. The speedo is a bit more touchy as it wants 11-15 volts to work. I've wanted a signal generator for awhile just to play around with, building up the custom cluster was the excuse I needed to finally buy one.