This has been beaten to death according to google, but there are a LOT of answers/solutions.
My biggest issue is that I'm very new to all of this and just started working with electronics this year.
I have 3 separate systems that all output a 12v square wave signal intended for an automotive Tachometer. All at separate duty cycles, but basically the same 12v square wave in a similar frequency range.
I need a simple solution that will work for all 3 sources so I'm not constantly switching based on which I am using at the time.
It looks like a voltage divider is the way to go for dropping the signal down to a useable 5v. I'll have to slightly overcompensate thanks to automotive voltages being as high as ~14v in any of these systems.
The next part is the confusing part. I would like to use a L7805CV. Its a linear voltage regulator that will limit it to 5v. I've heard a lot of people say I will need to use a heatsink thanks to the amount of heat that will be generated in a 14 to 5v drop. Since the maximum amperage on a digital pin on the arduino is only 40mA, I should only be looking at a maxiumum of .36 watts as heat.
Am I OK only using the voltage regulator, or should I look into other solutions? I'm just looking for the least complicated solution. If 2 resistors are giving some people success, can I not use a single voltage regulator?
JoeNova:
I would like to use a L7805CV. Its a linear voltage regulator that will limit it to 5v. I've heard a lot of people say I will need to use a heatsink thanks to the amount of heat that will be generated in a 14 to 5v drop. Since the maximum amperage on a digital pin on the arduino is only 40mA, I should only be looking at a maxiumum of .36 watts as heat.
To drop the 12v-14v square wave signal down to 5v for an Uno.
I'm basically looking for a one-shot deal, not a string of capacitors, diodes, and resistors. I don't want to have to order several different components, make a soldering mess, and have packaging issues since my Uno is already in a fairly slim case to begin with.
I guess my main question is, can I use an L7805CV to connect a 12-14v square wave signal to my Uno, or will I need more?
I don't think that a voltage divider is the way to go since the voltage you are using varies from 12vdc to 14vdc. that means voltage out of the divider is going to change too.
if you were to use the divider into a linear VR or maybe a buck converter (idk how those would operate with PWM)
If you want to read a 12-14V pulse signal using an Arduino input, a voltage divider is the way to go. A regulator is not the way to go.
The above mentioned 22K/10K divider divides by 3.1. Any signal on the divider input greater than about 10V will be registered as HIGH on a digital input.
For extra safety in the electrically very noisy automotive circuitry, put a 5K resistor between the voltage divider tap and the digital input, and do not power the Arduino directly from the automotive "12 V" socket.
jremington:
If you want to read a 12-14V pulse signal using an Arduino input, a voltage divider is the way to go. A regulator is not the way to go.
The above mentioned 22K/10K divider divides by 3.1. Any signal on the divider input greater than about 10V will be registered as HIGH on a digital input.
For extra safety in the electrically very noisy automotive circuitry, put a 5K resistor between the voltage divider tap and the digital input, and do not power the Arduino directly from the automotive "12 V" socket.
Yes, I'm just looking to read the frequency. I'll figure out the software side later, for now I just need to be able to connect the 12-14v square wave signal to my arduino without frying it. If I have to use a voltage divider, this is fine. 2 resistors won't take up a great deal of room.
I know not to power the arduino from the automotive 12v.
The main point of this being that I've got the 0-5v analog sensors down. Now I want to try frequency. I'm just going to connect it to the arduino board, and view it in the serial plotter. If I can get it to match closely to what the actual RPM of the vehicle is, I'll consider it a success and move on.
JoeNova:
Yes, I'm just looking to read the frequency. I'll figure out the software side later, for now I just need to be able to connect the 12-14v square wave signal to my arduino without frying it. If I have to use a voltage divider, this is fine. 2 resistors won't take up a great deal of room.
I know not to power the arduino from the automotive 12v.
The main point of this being that I've got the 0-5v analog sensors down. Now I want to try frequency. I'm just going to connect it to the arduino board, and view it in the serial plotter. If I can get it to match closely to what the actual RPM of the vehicle is, I'll consider it a success and move on.
Was it a success? I am trying to do the same. Please give me some pointers thanks.
A voltage regulator cannot switch fast enough to follow a fast pulse stream, use a voltage divider, for up to 15V, R1 = 22k, R2 = 10k, at 12V, divider junction will = 3.84V.