A few weeks back I successfully completed my first PCB board thanks to the help I got from this forum. It runs very well. But now that I got to this point I would like to add some features to it. The board is an automotive radiator PWM fan controller. The controller uses an Arduino 33 BLE that is powered up by the ignition switch through a timer relay. The timer relay is and external relay allows the radiator fan to run for some time after the ignition is turned off. You can see the link to that relay here:
So one of the upgrades I would like to add to my PCB assembly is the functionality of that timer relay:
I found this article on the web and was successfully able to get the circuit to power up the Arduino and hold it running for the specified time set by the combination of resistors and capacitors.
Great, I thought, but then I went to implement it and I realized the switch in the circuit shorts to ground and I only have an ignition switch that can power the circuit with ~14V.
From my automotive background, I know how to deal with this using a relay, typically with huge 30A currents or so. And in fact the relay I am using is an over kill 30A rated relay. So I figured I might be able to use a SS relay and so far I found a relay from Altran Magnetics, ASR-SMD48D0.1P that looks like it might work.
But my question is, might there be a different way to connect the 555 timer so it will switch with 14V applied directly to a pin. And if not is a SS relay the way to go or perhaps a transistor or Mosfet?
So in the diagram below, what are my options to connect the line "14V Key On" to.
Using the output of an NE555 as the power supply of an Arduino board? That's...yuck! Ugh. I'd buffer that with a P-channel mosfet.
It's not clear to me what you want to achieve, but you can feed those 14V into pretty much anything if you use a suitable resistor divider or ensure that the device you feed the 14V into will handle it.
To...what?
You have a very long story and my intuition says it should be a very simple issue, so could you try explaining it again but in two sentences max?
Going by what I can muster from the word salad, it seems you want to run an Arduino (and probably have it do something; control the fan?) for a certain time after the ignition key has been turned off.
Why not power the Arduino from the permanent 12V/14V and feed the switched 14V into one of its input pins through a voltage divider so that the Arduino 'knows' when the car is on, and the Arduino itself can remain on all the time. You can put it to sleep when the ignition is off and have it do its task when ignition is on and immediately after the ignition has been turned off.
I don't see the need or any advantage to having a 555 in there, and certainly not as a power supply for an Arduino...
Is there a better alternative to the NE555. What makes it yuck? Can you tell me where the base emitter and collector of the mosfet would get wired to?
I do apologize for some reason the link with the original basic circuit diagram did not get posted. I edited the first post to include the diagram and I will repeat it here. The circuit shown below was used to test the operation of the timer function by replacing the LED and 220KΩ with the Arduino.
The problem is that circuit activates the 555 timer by shorting pin 2 and various other component through a RCL network to ground. The last picture I posted shows the same circuit with the addition of "14V Key On" wire not connected to anything. The goal is to replace the mechanical switch that grounds circuit and activates the 555 timer with an electrical device that is powered by the "14V Key On".
Running the Arduino at all times is an option. This particular car may not be started for several months at a time especially during the winter. The car battery will generally start the car after 3 or 4 months of storage. What should I expect for storage life reduction if powering an Arduino 24/7.
A 555 is not a power supply. An Arduino is a board that can have an erratic and sometimes relatively high (depending on the board used) current draw and logic IC's such as the 555 simply aren't made to supply that. If the Arduino for whatever reason draws a peak current, the 555 won't keep up and the microcontroller will go into a brownout condition. Especially with something wireless-enabled such as a 33BLE.
Google 'p channel mosfet high side switch'
Replace switch with any small signal N-channel mosfet. Google 'n channel mosfet low side switch'.
Having an Arduino board in a car for this kind of thing makes little sense to me, but you can work out the power demand by referring to the datasheet of the microcontroller. You'll probably have it in its deepest sleep mode with a typical current draw for modern microcontroller in the range of 5 ~50uA from the top of my head. With an Arduino board you have considerable losses in all the peripherals and the power supply, especially with something like a 33BLE, but all in all it won't drain a car battery in halfway decent condition in a year or so. You'd have to do the math on it and I'm going to leave that to you.
What does the 33BLE board actually run in this system? Is it just the fan controller that we've seen before? As far as I can recall that would run fine on a bare ATMega328PB (or whatever you fancy) which you could plant on a custom PCB and have it run without a 555, with a buck DC-DC converter. If you're going to make a custom PCB anyway you might as well do it right instead of knitting together a string of modules.
Sounds like its a minimal draw and worth trying it out with Arduino on 24/7. Certainly simplifies things. The only thing the Arduino runs is a 10Hz PWM fan controller along with several LED outputs to blink out thermister temperature ranges. I will be using BLE to transmit those temperatures to my cell phone but only when the car is running. But of course none of those are running when the car is off.
Yes you may have seen this fan control in other threads most likely this one:
BLE is not used at the moment, but I'm working on getting that to report temperatures to my cell phone. A nice feature since the control is mounted where I cant see it. I kind of suspected that any of the Arduino Boards have a lot more baggage than I need and that a simple chip could be substituted in place. But I need to walk before I run and it was just about 6 months ago where the only thing I could do was get a light to blink. So for the moment I will stay with the Arduino, but not adverse to trying different things at a later date.
Definitely going to try the Arduino on for 24/7. I already planing another circuit to sense engine off with key on. I believe I can use it to run the Arduino for a set amount of time in the shut down mode as well.
The need for this circuit is required in the event that if I have the vehicle warm and the engine is off, but the key is turned on for any reason like listening to the radio, I still need to provide a 10Hz 10% PWM signal to the fan to keep the fan from running. This is required because the Mercedes Benz fan has a completely separate circuit, that with the key on applies a 12V signal to the fan motor, which will run the fan at 100% emergency mode in the absence of any PWM signal below 10% duty cycle. 10% duty cycle turns the fan off and the fan only runs in programed mode from 20% to 90%
I can also use this circuit to trigger the programed run time after shut down.
I haven't tested or vetted this circuit on this forum yet so comments on it are welcome.
One of the nice things about this is that if the Arduino proves to be too much drain over time, I can still install the external Beuler time delay relay.
