MS3 speedo output

[arran]

Hey all,
I'm thinking about using an MS3 feature in Speed and Gear Sensor menu "VSS output". Hopefully a really simple question: it does work OK yes?

Just thought I'd ask about any known problems before I spend a buch of time and a little bit of money on installing stuff in the car to a certain design and then find that something is broken.

I want to replace the speedo cable in my RX7 with a speed sensor (I have one that fits the gearbox). The pulse train is sent to MS3, and with any luck I can scale the frequency of VSS out for easy calibration. VSS out would go to an Arduino, there are libraries available for a conversion to PWM which is then a no brainer to drive a brushless motor which turns the speedo mech.

Thanks

[edgedj]

yup, it works

[jsmcortina]

VSS out would go to an Arduino, there are libraries available for a conversion to PWM which is then a no brainer to drive a brushless motor which turns the speedo mech.

You can use the MS3 to generate a PWM output based on VSS already. Use Generic PWM with a curve and VSS.

James

[arran]

Thanks and thanks

[arran]

Is there any way to increase the frequency? 250Hz seems to be the fastest.

I can't find a PWM controlled motor that goes that low. 500Hz would get me out of trouble

[arran]

Still curious if there is a way to increase Generic PWM frequency. Most motors operate in the kHz range, 250Hz is quite low. For example, very inexpensive and accessible brushless motors and BLHeli_S electronic speed controllers run PWM at 24kHz

Thanks in advance

[jsmcortina]

The Generic PWMs are generated using software PWM and therefore the max frequency is limited. The processor used in MS3 has a set number of hardware and the frequencies are linked to each other.

James

[billr]

I'm a bit confused about what the intent is for higher PWM frequency. I think of PWM as being a means to achieve variable DC voltage levels, with the end frequency being essentially "zero". Yes, I am aware that PWM is often used with no electrical filtering, relying on mechanical response of the driven devices to "filter"'; but proper electrical filtering could be added if needed for a particular application.

[jsmcortina]

The downstream devices are almost certainly handling this digitally and measuring the pulsewidth, period, frequency.

James

[arran]

After a bit of delving into the depths of Aliexpress, I think I might have come across a reasonably simple solution.
This is a frequency controlled motor. Aside from maybe needing a regulated power supply, it can be driven directly from the Megasquirt Speedo out function. It's minimum rotational speed is listed as 150 RPM which in my car equates to about 15kph which is acceptable. It is a little larger than I'd like as there isn't a lot of room behind the cluster, but that might be a good thing as it should be able to provide adequate torque to spin the cluster. It is cheap enough at about AU$10 delivered. Worst case it can be mounted in the engine bay and coupled through to the back of the cluster through the hole vacated by the existing cable. It is a straight shot.

https://www.aliexpress.com/item/DC-12-2 ... 88657.html