# Circuit / component design help needed **URL:** \ **Category:** General Guidance\ **Created:** [February 14, 2024, 8:24pm UTC](https://forum.arduino.cc/t/circuit-component-design-help-needed/1223996 "2024-02-14T20:24:26Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![modularfox](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/modularfox/32/1013044_2.png) [@modularfox](https://forum.arduino.cc/u/modularfox)\ **Post date:** [February 14, 2024, 8:24pm UTC](https://forum.arduino.cc/t/circuit-component-design-help-needed/1223996/1 "2024-02-14T20:24:26Z")
Hi, Im working on another project. I have an OEM gear shift circuit that has a sliding contact which connects ground to the corresponding gear position and in the original circuit, it lights up the led. I need to tap into the Reverse Ground signal, and the output signal can only be ground. The issue is, when its not in reverse, I measure anywhere from 4v to 7.5v on the Reverse signal wire as I change gears - Reverse to Neutral to Drive Maybe some type of diode if so which one? Clint ![20240213_173801](https://europe1.discourse-cdn.com/arduino/original/4X/7/3/d/73d94989a015e9efee848d61793b1620f49dfa60.jpeg) ![17079425787794684975885248775414](https://europe1.discourse-cdn.com/arduino/original/4X/f/0/c/f0c9644d283d82351a72f30609a05d6847516e06.jpeg) ---
**Author:** ![PerryBebbington](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/perrybebbington/32/238766_2.png) [@PerryBebbington](https://forum.arduino.cc/u/PerryBebbington)\ **Post date:** [February 14, 2024, 8:37pm UTC](https://forum.arduino.cc/t/circuit-component-design-help-needed/1223996/2 "2024-02-14T20:37:15Z")
Have you connected the ground? ---
**Author:** ![modularfox](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/modularfox/32/1013044_2.png) [@modularfox](https://forum.arduino.cc/u/modularfox)\ **Post date:** [February 14, 2024, 9:27pm UTC](https://forum.arduino.cc/t/circuit-component-design-help-needed/1223996/3 "2024-02-14T21:27:01Z")
I did not try and connect it to the other circuit. When I peeled back the insulation on the wire for reverse signal, and when I measured voltage present, I was thinking it would damage or mess up the other circuit Im connecting it to. Defiantly don't want to fry anything The circuit I need to send the signal to is the Instrument cluster, when it gets ground signal, the cluster transmits a message to another module and it turns reverse lights on. I've coded the cluster from Auto to Manual transmission and the reverse light diagram for manual transmission is: Ground -\> switch mounted on transmission -\> to instrument cluster When reverse is selected, switch closes and sends ground to cluster, otherwise open. So, I just need to tie in to the reverse wire that turns the LED on, but I only want to see ground or open circuit on wire i tie in (so I don't damage the instrument cluster) clint ---
**Author:** ![PerryBebbington](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/perrybebbington/32/238766_2.png) [@PerryBebbington](https://forum.arduino.cc/u/PerryBebbington)\ **Post date:** [February 15, 2024, 5:15am UTC](https://forum.arduino.cc/t/circuit-component-design-help-needed/1223996/4 "2024-02-15T05:15:42Z")
Sorry, but I find your description unclear, please post a schematic showing how you have everything connected, hand drawn and photographed is fine. You say you measured the voltage, between which 2 points did you measure? You might find this useful: > [@Common ground and why you need one](https://forum.arduino.cc/t/common-ground-and-why-you-need-one/626215): > > A common mistake for people new to electronics is to have 2 circuits fed from different power supplies with signals passing between the circuits, but with the grounds not connected. This leads to questions asking why the project doesn't work. You don't have to spend long reading the questions on this forum to see this is asked often. Here I attempt to explain the problem and why it matters to connect the grounds. Note that in all of the schematics that follow I have used a battery as a power sup… ---
**Author:** ![johnerrington](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/johnerrington/32/340106_2.png) [@johnerrington](https://forum.arduino.cc/u/johnerrington)\ **Post date:** [February 15, 2024, 7:09am UTC](https://forum.arduino.cc/t/circuit-component-design-help-needed/1223996/5 "2024-02-15T07:09:40Z")
what do you intend to connect the signal to? Why is the voltage a problem? ---
**Author:** ![modularfox](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/modularfox/32/1013044_2.png) [@modularfox](https://forum.arduino.cc/u/modularfox)\ **Post date:** [February 16, 2024, 1:04am UTC](https://forum.arduino.cc/t/circuit-component-design-help-needed/1223996/6 "2024-02-16T01:04:50Z")
The pictures is the factory gear shifter position circuit that lights up the factory LED board... all OE factory (besides me cutting the reverse signal wire for testing) I just want to tap into the reverse LED ground signal to send only ground when in reverse to the instrument cluster. But when testing (wire striped back and just checking with volt meter, - one lead on chassis ground and other on the reverse LED signal when moving shifter to other gears, it had 7 some odd volts when not in reverse. Ill get a video tomorrow illustrating this.. I think the Factory circuit is just back feeding? and has no effect on anything else since in the factory/original circuit it would only be connected if it were in Reverse. @johnerrington , conect to the instrument cluster, it is expecting ground or open circuit on the input pin. I don't know what would happen if it got voltage, I just rather not "just send it" as it would be expensive to replace. I'll try and update tomorrow evening with the video... Worst case - I just leave the reverse signal open, not connected to the Factory circuit board (led will not light up) and just use that ground signal for the Instrument Cluster.. kinda want to avoid this but its an option. clint ---
**Author:** ![Wawa](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/wawa/32/1211303_2.png) [@Wawa](https://forum.arduino.cc/u/Wawa)\ **Post date:** [February 16, 2024, 1:46am UTC](https://forum.arduino.cc/t/circuit-component-design-help-needed/1223996/7 "2024-02-16T01:46:49Z")
The safest way to tap into an existing board is with an opto coupler. Connect the opto LED (with current limiting resistor) across the indicator LED or across the voltage that powers the indicator LED+resistor. You only need 1mA or so for the ~1.2volt opto LED. Connect the opto transistor between an Arduino digital pin and ground, with pull up enabled. Leo.. ---
**Author:** ![johnerrington](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/johnerrington/32/340106_2.png) [@johnerrington](https://forum.arduino.cc/u/johnerrington)\ **Post date:** [February 16, 2024, 6:51am UTC](https://forum.arduino.cc/t/circuit-component-design-help-needed/1223996/8 "2024-02-16T06:51:40Z")
I'm guessing you are doing this to make a simulator - not using it on a vehicle? ---
**Author:** ![modularfox](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/modularfox/32/1013044_2.png) [@modularfox](https://forum.arduino.cc/u/modularfox)\ **Post date:** [February 18, 2024, 5:13pm UTC](https://forum.arduino.cc/t/circuit-component-design-help-needed/1223996/9 "2024-02-18T17:13:25Z")
this Isnt for a simulator, its for my engine swap that I've done 9+ years ago and finally want reverse lights to work. @Wawa thank you for the octocoupler idea. I had several 4n35 from a previous project. I had an old USB cord for testing with 5v power supply power bank. When testing, it had about 170Ωwhen connecting ohmmeter ground to pin 5 of the chip. I wasn't sure that would be good enough so decided to try it since its only ground signal. Not sure if a different octocupler would have a lower ohm value + this is in a cheap cheap breadboard that might be contributing to it. 5v power supply + 370Ω to pin 1 ground to pin 2 instrument cluster (waiting for ground ) pin 5 ground to pin 4 when pin 4 is connected to ground, It worked when using a 5v cigarette lighter (so it shares chassis ground) now to find a resistor value for 12v to power the octocoupler and test again thanks for everyone's help and ideas clint ---
**Author:** ![system](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/system/32/1140315_2.png) [@system](https://forum.arduino.cc/u/system)\ **Post date:** [August 16, 2024, 5:13pm UTC](https://forum.arduino.cc/t/circuit-component-design-help-needed/1223996/10 "2024-08-16T17:13:57Z")
Closed on August 16, 2024, 5:13pm UTC This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.