Timer function for 1 hour

Thread Starter

FroceMaster

Joined Jan 28, 2012
636
Hi,
Need a little timer function for my curcuit.
Timer.png
When 12v is provided at the "left" the curcuit should open for LOAD.
When 12v is missing again the curcuit should provide open LOAD for ~1 hour.
 

wayneh

Joined Sep 9, 2010
16,500
So you want a one hour delayed turn-off. Can the timer circuit use the same power source as the load?

What range do you mean by "~1 hour", eg. ± 5 minutes?
 

Reloadron

Joined Jan 15, 2015
5,714
When 12v is provided at the "left" the curcuit should open for LOAD.
When 12v is missing again the curcuit should provide open LOAD for ~1 hour.
Open for load implies the load is turned off or open circuit? I am not understanding the terminology you are using?

Do you mean when power is applied you want the load turned on and when power is removed you want the load to remain on for one hour? Should that be the case it sounds like what you want is a "delay on break" timer function. You can buy a simple inexpensive timer or roll your own. A Google of "Delay On Break" or also called Off Delay, Delay on Release, Delay on De-Energization should yield some solutions. I also suggest you read these definitions paying attention to the timing illustrations to determine exactly what you want by definition. Then consider as mentioned above the allowable tolerance you can use.

Ron
 

Audioguru again

Joined Oct 21, 2019
2,374
A door opens and closes.
An electronic circuit turns on or it turns off.

When 12V is applied to the timer then I guess you want the load to turn on for one hour then turn off.
Then when the 12V is disconnected from the timer nothing will happen because your timer will not be powered.
 

ErnieM

Joined Apr 24, 2011
8,078
There are "time delay relays" that will do the task with little effort.

If you really desire to roll your own timer look into the 4060 CMOS 14-stage binary ripple counter and oscillator. Basically you set up it's RC oscillator to count to the time. Very long times can be made. In fact, Deutch Relays used to use these in their MIL time delay relays. I know because my company built them to print.
 

Tonyr1084

Joined Sep 24, 2015
5,515
The +12V for the timer; is it the same source for the +12V for the load?

Do you want the load to remain operating (on) for approximately one hour AFTER the timer has shut off?

Really, what I'm seeing is a timer that controls a transistor (switch). If the timer is off (no 12V) then there is no power to the transistor; and the load will shut off. On the other hand, if the 12V to the load is shut off, it wouldn't matter what state the transistor is in because there is no power for the load.

A little more clarity would help. More specific information is needed. At least I need more info before I can begin to help.
 

Thread Starter

FroceMaster

Joined Jan 28, 2012
636
Ok a little clarifycations..
I want a curcuit that operate the "LOAD" that i my case is a DashCam.
I want it to stay recording for aproximate a hour after the 12v is missing,( Car stopped )
If i have to use CD4060 and some components, i could easy make a Microcontroller and a transistor, less components.
 

jpanhalt

Joined Jan 18, 2008
10,933
I would run the dash cam from a continuous/uninterrupted power source (i.e., one that stays on when the key is removed), such as an accessory plug (probably depends on car model). Then you need to detect "key on" or any similar signal that is available. Models may differ. That signal may be at the OBD plug, but you probably do not want something plugged into that continuously.

Once you identify that signal, then when it is sensed, you enable the camera. The camera may have separate power and enable connections. For example, it may have a clock function that runs continuously while the camera function is off. When "key on" signal goes low, start a countdown to turn camera off.

A simple MCU operating with a 32.768 kHz crystal for a timer, say Timer1, will give 2 seconds per "click" of a 16-bit timer (e.g., Timer1). You can add a prescale of 1:8 to give 16 seconds per click and count those clicks to 225 to give 1 hour. By using various pre-scales and post-scales, you can do everything with simple 8-bit registers. Or, you can get a little more complicated and create a 16-bit register. In either case, it will not require a very sophisticated MCU and your timing will be fairly accurate compared to trying to get a long period like that from a 555 timer. If you don't want the MCU, then a 555 timer with a counter chip can do the same thing.

It is time for you to give some details.
 

jpanhalt

Joined Jan 18, 2008
10,933
Pin4 is MCLR. You probably want to tie that high if MCLR is active, and because automotive circuits are noisy, you will want adequate decoupling. I assume the simplifications in your schematic are intentional.
 

ErnieM

Joined Apr 24, 2011
8,078
If i have to use CD4060 and some components, i could easy make a Microcontroller and a transistor, less components.
That solution is ultimately what I proposed to our customer. It made a single assembly module work for all the many configurations and timings they required. Unfortunately their CEO was concerned about "the program memory loosing the code" and the project languished... until their major competor came to us asking us to design them a solution.
 

Tonyr1084

Joined Sep 24, 2015
5,515
Here's something I've come up with a month or two ago. MY desire was to be able to enable the camera to remain recording while I was in the grocery store (or any parking lot). MINE turns the camera on and keeps it on until I step on the brake pedal. The relay is activated by SW1 only when the key is in the on (run) position. K1 then holds itself on, grounded through the brake light bulbs. When I come out of the store and start the car, the first thing I do is step on the brake pedal. This cancels K1. But with the key on the camera is still powered while I drive. When I get home I DON'T trigger the camera. Who wants to record all night inside the garage? So 5 minutes, 15 minutes, an hour or more, the dash cam continues to record until I return. Then it continues to record while I drive. But when I shut the car off the camera shuts off too. Maybe this may spark an idea for you.
1610292532153.png
 

jpanhalt

Joined Jan 18, 2008
10,933
You might want to reduce the 5k (R1) a bit. Assume an hFE of just 10 or use a logic level mosfet. If you use a mosfet, you might also want to include a 10k turn-off resistor.
 
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