Arduino current sensing (in car)

[Curious.George]

Re: Arduino current sensing (in car)

i often wonder why they and other company's dont simply exploit every function in the chip.

Often, it allows them to differentiate among current (as well as future!) "models" in their lineup. What's most annoying is when an upscale model differs solely from a "basic" model because of a "hidden" internal setting!

There are nonrecurring (development) costs associated with each feature you implement. Plus, potential recurring (manufacturing) costs -- additional knobs, buttons, extra pages in a manual, etc.. And, the "commitment" they must now make to supporting that functionality going forward ("design maintenance").

But, there is also some value to not offering extra functionality as it keeps the user interface (cognitive loading) simpler. You don't have to provide a way to differentiate among several different features in a single interface AND task the user with remembering those subtleties!

E.g., the Unisite's "high level" user interface is provided via a user-provided glass TTY (typ ANSI 3.64). The Unisite, itself, has just two buttons on it: power (obvious) and a button that basically swaps RxD with TxD in the serial port connector on the rear of the instrument. So:

• plug in cable
• tap space bar (so Unisite can determine proper parameters for the serial port)
• if no reply, push button to swap RxD&TxD and repeat

Other devices with serial ports would typically leave the user wondering what cable to use (wired as DCE or DTE?), baud rate, stop pits, parity, etc. And, do nothing to solve this problem FOR the user ("Hmmm... that cable didn't work. Let's try a different one -- and hope that none of the other settings are the reason for the cable not working!)

Of course, they COULD have exposed all of these settings to the user in the guise of "more flexibility/capability" (what happens if I want to talk to the device using EBCDIC?). Thankfully, they didn't let the engineer(s) make that decision! (who invariably opt for more knobs and settings)

Similarly, the electric wheelchair I'm tinkering with has a serial port supported by the controller (it's actually labeled on the PCB). Why not document how that interface works so I can tinker with the controller's "buried" configuration settings?

[stj]

Re: Arduino current sensing (in car)

Cool thanks. How'd you come up with those BTW ? I read about part of them and trying finding more, but didn't dig deep enough apparently. I assume it's all optional though - I don't HAVE to modify anything if I'm satisfied with the "defaults" I suppose.

Also, when you say for instance DC>AC, does that mean it starts up in default DC or defaults to DC when x function is selected ? That would indeed be handy in some situations. I reckon mine has the 1106 in it, though I only say this because I've seen some pictures of its guts - haven't opened MINE up yet to know exactly.

the memory locations are from older research for the Aneng meters,
but they mostly apply to anything using that chip - the UT-139c for example

and you got it correct, you can change the order it runs through, so it starts on your most used setting.

[stj]

Re: Arduino current sensing (in car)

in the case of the wheelchair, it may be a legal thing.
some country's set safety limits on how fast wheelchairs and mobility scooters can move.
personally if i had one i would mod it like the one in one of the Mr Been comedy films - that "turbo mode" could be handy!

[Curious.George]

Re: Arduino current sensing (in car)

in the case of the wheelchair, it may be a legal thing.
some country's set safety limits on how fast wheelchairs and mobility scooters can move.
personally if i had one i would mod it like the one in one of the Mr Been comedy films - that "turbo mode" could be handy!

Yes, it's a legal thing -- but one of liability (not speed limits, etc.)!

Most electric wheelchairs, powerchairs, mobility aids are configured to be overdamped control systems (with the human being the controller). The thinking being to attenuate the responsiveness so the user doesn't screw up and find himself in the middle of the road during rush hour!

As a result, they are typically "programmed" (configured) to be more sluggish. Often, you "move the stick" and WAIT for the chair to respond (the delay is entirely artificial and can be "unconfigured").

Imagine what would happen if the auto manufacturers would let users tinker with the control algorithms for their ECU's which are also "configurable" to a very fine degree of detail -- in ways that can provide increased (or decreased!) performance, fuel economy, safety, etc.. Simpler (from a lawyer's perspective) to make them "closed" systems than to have to first prove that the plaintiff mucked with his car's computer(s) prior to the "deadly accident"!

As to "turbo mode".... you'd be surprised at how hard it is to control a chair even traveling at 6 MPH! (most max out around 4MP). This is one reason why chairs offer "configuration profiles" (think: indoor use, outdoor use, etc.)

[Dannyx]

Re: Arduino current sensing (in car)

Just to let you guys know, whoever is following the thread that I have been working on the code all this time and got the bulk of it down...just need to add a couple of more features and then work on the most challenging part which is going to be the current sensing. The topic's not dead that is

[Dannyx]

Re: Arduino current sensing (in car)

Today I measured the current drawn by the windows (having put back together my Uni-T UT210E clamp meter I messed around in another post) and it's around 4-6A when the windows are moving freely and around 12-15A when they reach the end and stall. Just as suspected, there's no cutoff at that point - as long as you hold your finger on the button, it will keep drawing that current...until maybe either the battery dies out or there's some thermal cutoff in the motors themselves. This makes my job easier, because I initially feared there would be some cutoff in the motors that kicks in immediately and cuts the power (despite being positive the wires run straight into the motor without any circuitry in between), which would mean the stall current would only be present very briefly and I'd have a very small window to "capture" it and tell the thing to stop, whereas with this unmonitored setup, it's much easier to capture it. I'd say a "trip point" of around 10A is ideal - not too high, not too low.

At least now we have a baseline, so we need a 20A H-bridge (which I found here) and a current sensor. Found one here as well....liking this bangood more and more

Code is also starting to take shape. Just a couple of more kinks to work out and then I can try prototyping with a large enough motor to simulate the actual motors as closely as possible. Found one at work in my junk bin...will have to think of a way to apply load to its shaft since it's got a metal gear on it (presumably came out of a drill or something) and it'd chew through anything I'd try to brake it with...anyway. Cheers guys

[sam_sam_sam]

Re: Arduino current sensing (in car)

I messed around in another post) and it's around 4-6A when the windows are moving freely and around 12-15A when they reach the end and stal

Found one at work in my junk bin...will have to think of a way to apply load to its shaft since it's got a metal gear on it (presumably came out of a drill or something) and it'd chew through anything I'd try to brake it with...anyway. Cheers guys

Why not use a couple of car head lamp and use low and high beam at the same time until you reach 15 amps

[Dannyx]

Re: Arduino current sensing (in car)

Will that even be enough ? I'd need a lot of them, which I don't have sadly.

[sam_sam_sam]

Re: Arduino current sensing (in car)

You might need 3 or 4 head lights
Do you have a car junkyard near where you live you can get them cheap

[stj]

Re: Arduino current sensing (in car)

if you want a load, or a current limit, use a mains halogen flood light.
they are very cheap because most people want leds instead now.
very handy if you want 120w,300w,500w etc.
i use one as a current-limit for "first-time" testing.

[budm]

Re: Arduino current sensing (in car)

Check the cold resistance of the lamps first.

[stj]

Re: Arduino current sensing (in car)

30ohms (120w)

[budm]

Re: Arduino current sensing (in car)

Is that hot or cold resistance? 30 Ohms 120W
30ohms (120w) = 60V @2A

https://www.rapidtables.com/calc/ele...alculator.html

[budm]

Re: Arduino current sensing (in car)

Check the cold resistance of the lamps first.

[stj]

Re: Arduino current sensing (in car)

that;s cold.
so 2kw using that calculator.
but will increase fast once it glows.
so better than nothing.

[budm]

Re: Arduino current sensing (in car)

If 30 Ohms is cold resistance then hot resistance will be more than 10 times higher, that will not be 120W lamp for sure.
So all Dan has to do is to measure the cold resistance to know what the surge current will be, it will last in mSec which hopefully will be shorter time the over current protection circuits to detect.

[stj]

Re: Arduino current sensing (in car)

sold as 120w!
https://www.rapidonline.com/brennens...44-120w-533066

[budm]

Re: Arduino current sensing (in car)

OK, 30 Ohms cold then the inrush will be 230V/30 Ohms =7.67A
120W at 230V = 440 Ohms, so the hot current = 0.52A.
So 30 Ohms cold is about right then.

[budm]

Re: Arduino current sensing (in car)

BTW, so to use this 120W 230V LAMP as the load for 12V @30 Ohms cold resistance, the current will be <1/2A so he will need a lot of lamps.

[stj]

Re: Arduino current sensing (in car)

that one was an example, he could get them upto 2kw