I am trying to create a sort of sequential shift light. I have got all the lights set up. But i need to get input from car's RPM wire. I dont know whether I should plug it straight to analog input pin. Please guide me through it. Also whether i should power it via the car battery.
am trying to create a sort of sequential shift light. I have got all the lights set up. But i need to get input from car's RPM wire. I dont know whether I should plug it straight to analog input pin. Please guide me through it. Also whether i should power it via the car battery.
It depends. There are many different types of rpm wires. Some would damage the Arduino if connected directly. You need to know what type your vehicle has in order to be able to interpret the rpm signal. Some are analog voltage which vary with rpm, some are pulsed digital signals, some are AC signals...
That's a recipe for damaging something.
First you need to know what kind of signal is present. Do you have any relevant information about the RPM
sensing?
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Thanks in advance for your cooperation.
UKHeliBob:
Duplicate topics moved and mergedCross-posting is against the rules of the forum. The reason is that duplicate posts can waste the time of the people trying to help. Someone might spend 15 minutes (or more) writing a detailed answer on this topic, without knowing that someone else already did the same in the other topic.
Repeated cross-posting will result in a timeout from the forum.
In the future, please take some time to pick the forum board that best suits the topic of your question and then only post once to that forum board. This is basic forum etiquette, as explained in the sticky "How to use this forum - please read." post you will find at the top of every forum board. It contains a lot of other useful information. Please read it.
Thanks in advance for your cooperation.
Sorry didnt know that, wont repeat
I've never done anything like this before , but I might be tempted (assuming a petrol engine) to take a sense wire from the 12V side of the ignition coil through a suitable dropping resistor and perhaps a snubber behind a diode to an opto isolator with it's output connected to a pulled up digital input. A 4 cylinder engine would give 2 pulses per rev. Alternatively it should be possible to take a sense wire from the rev counter again through a resistor and optocoupler. The pulse rate will vary proportionally with the rpm of the alternator which will be proportional to the engine revs, but may not be the same. It shouldn't be too hard to "calibrate" it to find the number of pulses per engine revolution. You've already got an engine taco and, it should be easy to make the arduino flash a LED for every pulse which can be read with with a cheap hand-held reflective taco with its LED taped over.
the RPM wire is the trigger for the ignition coil. on an older points type system, hundreds of volts. find a circuit for a tachometer, which isolates the trigger voltage from the tach, and add a mechanism to limit that to 5 VDC
Does the car have an OBD port? If it does you could use a ELM327 and just read the RPM from the ECU
Andym535:
Does the car have an OBD port? If it does you could use a ELM327 and just read the RPM from the ECU
Yes exactly, I have ditched the first plan and i have decided to take signal from ELM327 via a HC05 Bluetooth module. But for me a problem is the coding part ( I am a beginner). I dont know how to take the rpm values out in the code. How is rpm interpreted by the user? Can anyone give me some pointers? Like which keywords is used. I just need the rpm value and light up the leds accordingly. I think once i get the rpm value it is a pretty simple code even for me. Help me out.
Thanks.
Talking to an ELM327 is a bit like using an old modem, using hayes AT commands. You basically sent the ELM a couple of AT commands to reset, set the protocol and connect, then sent request codes. You'll then get the reply back as a response code. Data will come back as hex, you just need to convert to decimal and sometimes scale it to get a value.
Hookup Windows terminal to your ELM, connect to the car, ignition on, then type a few commands and you'll soon see how it works.