Speedo out to drive DC motor

[tobmag]

Since I have an old mechanical speedo meter in my car I need get that running as well some how.
I have added a small DC motor to drive the mechanical speedo on one of my cars but that incoportated a lot of work with the electronics...

It should be bossible to drive a small low rpm dc motor directly from the speedo output by removing the pull-up resistor and adding the fly-back diod?
The DC motor I'm looking at will only use 200mA


BR//Tobmag

[Matt Cramer]

The speedometer output is frequency based, but what you need here is a duty cycle based signal.

[tobmag]

Ok then it will not work, too bad since that would help many changing to newer transmissions.

But I could use SP1 or 2 in PWM mode using speed as index value?


BR//Tobmag

[tobmag]

I Have been doing some testing and it does actually work to drive a DC motor connect to the mechanical speedo.
Running SP1 in PWM mode.

The only thing is that it seems to be a hick-up in the code since the PWM signals and motor stops at every gearchange, up and down shifting.

BR//Tobmag

[tmoble]

Wow, tobmag, are you a genius or what? I've been wanting to find some way to do this ever since I first found a nice 4L60E. I have a 57 Chev pickup with 327 V-8 the tranny is going into, I would dearly love to keep the stock speedo working. I checked out the commercially available units and was gagging on sticker shock. I don't have that much in the entire conversion .

Would you be willing to disclose what motor and electronics you found to work? I never could figure a way to find the actual power needed to run the cable up to 1500 - 2000 RPM. Is it like 1/10 HP or something?

The only thing I ever knew was that a GM standard was in place that the speedo cable RPM was supposed to be 1000 at 60MPH.

Is that motor something a guy could buy on ebay or some other low cost vendor?

[tmoble]

would this be of interest? use PWM 0 - 5V to control 12V motor.

eBay link deleted per forum rules

[tobmag]

tmoble.

There is no need for any additional PWM control. You can use either SP1 or SP2 directly since they are capable of putting out a PWM signal, the driver can handle up to 7,5A if I dont remeber wrong.
Right now I use an old motor from a scrapped VCR player. Problem is that its not spinning fast enough just reaching 110mph and is not putting out high tourqe enough at lower speed so it will jump start to 20mph.

I'll pass by the local R/C shop and see what they have in terms of electric motors for R/C controlled cars etc. They should have something suiteble and they are usually very powerfull and depending of application spinning fast enough (i hope) thing there is that they are usually 7,2V but that you can controll by limiting the PWM signal.

I'm using the same VCR motor to another car I have and that one is working as a dream, different speedo though...

I hope Lance can explain why the PWM signal is dropping to zero when changing gears.

BR//Tobmag

[tmoble]

tobmag,

have you seen any evidence of Lance or forum admins logged on here recently? kinda looks like the activity has really died off here.

[tobmag]

I really appriciate all help/assitance from Lance but I need to admit that it is a bit scary when all support seems to be related to 1 guy only.
It makes you think if the GPIO board was the way to go for the tranny control, yes cheap but what does that help you if there is no or very limited support?
The concept is brilliant when you can connect it over the CAN to the engine management and very few manufactures out there today that can offer this.

But as with all these DIY things in the end it all comes down to the support......


BR//Tobmag

[Bernard Fife]

tmoble,

The PWM isn't supposed to drop to zero when changing gears (unless you tell it too using "Shift Line Pressure Settings": http://www.msgpio.com/manuals/mshift/V22tune.html#gl). So make sure you have those set appropriately.

I have been traveling the last week (to PRI to meet with Bruce and Al on various topics) but in general, I am slow to respond to post if:

- it doesn't not state the code version and include an MSQ and a datalog of the problem,
- it covers an issue already documented (http://www.msgpio.com/manuals/mshift/V22tune.html),
- it asks for information that I don't know (such as about a transmission that is new and unfamiliar to me),
- it asks about using the MShift in novel ways that the code was never intended to be used (in which case I will help if I can, but the user has to have explored all the current code parameters, and the come up with a proposed solution that I can implement in the code/hardware).

Tobmag, the current code is 100% documented. If I get run over by a bus, when the cheering stops users will have access to complete descriptions of all the parameters available on the web and in TunerStudio. This is entirely unlike some efforts, where the documentation lags months or years behind code releases.

Lance.