Thread: Way to convert a resisted Voltage output to a gnd signal over 2 channels

Ps: seems an arduino board will do what i want, but having read a little about them, it's beyond my current skills and available time (to learn). Anyone with a hobby interest to make one for me. Fair reward to be discussed.

I can think of 2 ways to approach it.

Yes, the Arduino is probably the easiest when putting stuff together you can buy off the shelf, although you'll need some input scaling or level shifting with an > 5V input. The software would be pretty basic.

The other is a more conventional pair of window comparators. One quad comparator, and a handful of resistors.

If I had some time I'd give you a hand, but you'd be better off finding someone local.

Voltage divide the input voltage using 2 identical resistors in series, eg 2 of 10K, to ground and pick-up the reduced voltage from the junction of the 2 resistors to reduce 9V to 4.5v. The Arduino or other microprocessor can convert the reduced analogue voltage to digital to then use a value range check to determine which shifter position has been used and trigger the appropriate output.

Originally Posted by Graeme

Voltage divide the input voltage using 2 identical resistors in series, eg 2 of 10K, to ground and pick-up the reduced voltage from the junction of the 2 resistors to reduce 9V to 4.5v. The Arduino or other microprocessor can convert the reduced analogue voltage to digital to then use a value range check to determine which shifter position has been used and trigger the appropriate output.

Of what little i understand of your description, i assume you are talking 2 circuits. first to reduce the 8.25v to 4.125v to bring it within the arduino <5v happy range (as an input). then code the ardruino to process the 2.88v into a channel 1 gnd output and 1.27v into a channel 2 gnd output. would i use the 4.125v to both power the arduino as well as be an input when in sports mode (and waiting for a momentary reduced voltage input). In that scenario, the arduino will only have power when the shifter is in sports mode and depowered when in the PtoD positions.

Even if i conceptually understand your wisdom, putting that into practice and making a gizmo is so far out of my skill set. I still need someone to do all of it for me. I reached out to a supplier of these parts to see if they would do it for me or point me in the direction of a skilled person. Any suggestions as to clubs, forums (other than Arduino that i stumbled across) etc that some budding and enthusiastic hobbiest will do the heavy lifting for me.

cheers Mark

The Arduino will need to be permanently powered, or at least with an ignition feed of 12V into a 5V regulator.
I'm not sure from your description of the operation of the 2 inputs whether the signals need to change from a positive voltage to 0V on a specific input or whether one needs to go positive and at the same time the other is 0V, but any combination could be catered for. If there is a need for 12V positive then that can be accomodated using a N-fet to drive a P-fet but if only minimal voltage eg 5V then use a weak pull-down resistor eg 10K and have the Arduino pull the pin high for the required duration (100ms perhaps?). If required to be low then use a weak pull-up resistor to 5V and have the Arduino pull the pin low for the required duration.
I've only quite recently been exposed to Arduinos, now using one with a satellite RTK correction module to inject extra records for the autosteer system in my tractor. The RTK module is designed as an Arduino hat hence the use of an Arduino, but I've been programming Picaxe microprocessors for the last 20 years.

Edit: Re-reading your last post, yes upon seeing an input value that corresponds to value 1 would pull output 1 pin low which would be pulled weakly high externally and the same for the other input value for the other output pin.
5V could be obtained from a USB socket.

Originally Posted by Graeme

The Arduino will need to be permanently powered, or at least with an ignition feed of 12V into a 5V regulator.
I'm not sure from your description of the operation of the 2 inputs whether the signals need to change from a positive voltage to 0V on a specific input or whether one needs to go positive and at the same time the other is 0V, but any combination could be catered for. If there is a need for 12V positive then that can be accomodated using a N-fet to drive a P-fet but if only minimal voltage eg 5V then use a weak pull-down resistor eg 10K and have the Arduino pull the pin high for the required duration (100ms perhaps?). If required to be low then use a weak pull-up resistor to 5V and have the Arduino pull the pin low for the required duration.
I've only quite recently been exposed to Arduinos, now using one with a satellite RTK correction module to inject extra records for the autosteer system in my tractor. The RTK module is designed as an Arduino hat hence the use of an Arduino, but I've been programming Picaxe microprocessors for the last 20 years.

Edit: Re-reading your last post, yes upon seeing an input value that corresponds to value 1 would pull output 1 pin low which would be pulled weakly high externally and the same for the other input value for the other output pin.
5V could be obtained from a USB socket.

Thank Graeme for taking the time to talk me through this. I'll try to answer your Qs as i understand them

1) I'll try to explain the GM auto shifter set up. On the underside of the shifter is a circuit board. Attached to the underside of the P to D shifter handle is an arm with a magnet. When you push the handle to the side to engage sports mode, the arm aligns itself with 3 pickups on the circuit board. By simply pushing the shifter across, the magnet rests over the middle pickup and i assume engages a circuit with a resistor. The output is 8.25v. Above and below the middle pick up is the pick up for the tap up and tap down. When you push the handle for tap up, the arm swings in an arch and the magnet locates itself over both the middle pickup and the tap up pick up to engage 2 resistors. The output is 1.27v. If you tap the other way, you get 2.88v. the 8.25v is a constant output while in sports mode but the 2.88v and 1.27v are a momentary switch. The duration of the 'moment' is as long as you lean on the shifter (spring loaded to return to centre). If you lean on the shifter long enough, it will trigger multiple gear changes (not good for the clutches but a function all the same). As far as i can tell the BCM doesn't need a long duration of the momentary switch and is programmed to be triggered when the voltage falls into a range +/- of the target voltage.

2) I assume the ardruino needs to ignore the 8.25v input (or a reduced voltage <5v if 8.25v is too high for the arduino to manage). When it receives a +/-2.88v input, it opens output channel 1 with a ground path for the ECM to receive a ground signal on one of 2 pins dedicated to the tap up or tap down. Receive 1.27v, it opens channel 2 to the other pin.

3) I don't need to use a 12v output, its an option that can be programmed in the ECM as a H or L input signal. The Holley documentation on how the ECM manages the tap up and down is silent and i do not know if it would recognise a 5v input or needs a higher voltage closer to the +12v. I could bench test it all but also mindful to not brick a $3000 ECM because of an experiment.

4) your edit describes what i'm trying to achieve.

If you have a word schematic that i can use to explain to a electronics wizzard with knowledge of arduino and circuit boards, i'd be most grateful. The parts supplier can't help, so i will kick the can down the road to find someone on a forum or the local Jaycar club meet to help me.

cheers Mark

If the Holley can be powered, check the voltage on the 2 inputs that need to be grounded to be selected to see if they are already above ground eg 3V, 5V, 12V. If they are already above 0V then the Arduino only needs to pull them to 0V without the need for resistors to pull them high.

I can help you but I need first to have a chat with one of my sons to find out if a particular Arduino board might be more suitable than others when other components need to be added, unless someone else here can advise.

This little $10 Arduino module has a 12V input so can be powered by an ignition feed, possibly from the same ignition feed to the GM shifter.
Arduino Pro Micro ATmega32U4 5V 16MHz Replace ATmega328 Pro Mini Leonardo USB | eBay
The 2 resistors required to reduce the GM signal voltage could be incorporated in the wiring to the Arduino.

Update: I have a Deek-Robot Pro micro for which I've written a program (sketch in Arduino-speak). I'll set-up a test for it over the next day or so. I suspect that the shift voltages are nominally 3v and 1.5v for which I'll have a range check that will cater for slightly lower voltages.
I've started with a 500ms hold to ground for a shift request then a 1 second wait to avoid multiple shifts unless really required. The ZF 6-speed in a D4 objects to a shift request longer than 1 second, which I discovered when building a shift module using wireless remotes for my D4 to simulate paddles direct to the gearbox shift request wires.

Another update: The boards that have an on-board voltage regulator barely suffer 12V but don't survive with automotive 14.4V, so one with a USB input is needed and therefore will require a USB socket or hard-wired 12V to USB.
It appears that I damaged my micro so I'll get one with a USB socket this time but I've proved the sketch on another Arduino that connects using a USB lead.