Dash Cam HOLD ON circuit

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,270
Last night someone hit my truck. No serious damage but I wish my dash cam had been on. Unfortunately it's only on when the truck is running. It HAS an internal battery, but that will deplete in short order if I try to run it in Motion Detection mode. So what I'd like to do is build and install the below circuit. It will not keep the camera running after I shut the truck off unless I push SW1 (hold) button while the engine is running. The camera will stay on until I step on the brake pedal. Obviously I won't be running it when the car is parked for hours on end; but when I run into the store for that quick pickup item, this won't harm the truck battery at all.

The plan calls for a relay - which I have plenty of them. However, I would like an electronic switch of some sort. As you can see, when energized, the relay will keep itself powered. The relay is chassis grounded through the incandescent brake light. If I step on the brake pedal and the brake lights light up, the relay is back-powered with positive feeds on both ends - the relay will drop out. So if at the store I push the button the camera will continue to record until I step on the brake pedal, which means when home the cam stops recording when I shut the truck off.

Condition 1) Engine off / dash cam off
Push SW1 - nothing happens.

Condition2) Engine on / dash cam on
Push SW1 - relay locks on - cam remains on

Condition 3) Engine on / dash cam on - step on brake pedal
Relay K1 drops out. Cam remains on until engine off.

Condition 4) Engine off (same as cond. 1)
1607362889128.png

What I would like to do is replace the relay with either transistor(s) or MOSFET(s). Any recommendations?
 
Last edited:

MrSoftware

Joined Oct 29, 2013
2,015
Would it serve the same purpose and be easier to just install a delayed-off circuit, that keeps the camera running for a couple of hours after you turn the key off? The camera drain on a car battery should be insignificant for that amount of time.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,270
MrSoftware hadn't considered that. Thanks for the suggestion. Will explore. Shouldn't need more than a half hour. A full hour may be useful when shopping with the wife.

[edit] but then when I park the truck I would have an hour of video inside the garage. I still think I'd want something I can set, like a trap, only when I want it. Maybe I can incorporate such a trap as set when pushing a certain button. Much less messing with the vehicle wiring too.
 

Hemi

Joined Mar 17, 2012
22
I like MrSoftware's suggestion. I think the default behavior should be to record unless you cancel it. Otherwise, your truck will get hit again only when you've forgot to arm it for that quick run into 7-Eleven. ;) A bright LED next to the button to cancel the delay would remind you to shut it down when you park in your garage.
 

PadMasterson

Joined Jan 19, 2021
29
Not sure on the year of your truck, but many of the newer systems run the accessory plug, (cigarette lighter) for about 20 minutes after the ignition is turned off. There is a relay circuit that does that function. I run mine from that outlet but I have a switched plug that when I get in the truck, I just flip the switch on, and turn it off when I'm parked in the garage. If I'm out and about and don't plan on being out of the truck for more than maybe an hour, I just leave it on, the system will shut it off after ~20 anyway. Just a thought. BTW, Sorry about your truck getting hit, I hope no one was hurt and the damage can be fixed.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,270
My Tacoma (2017) hasn't been hit. I just want to be sure there's a chance if someone does something I can possibly record the event. Since the camera points out, if I see someone pull into a parking space next to mine (if I've backed in) then I will have a record of who arrived and what time my truck was hit. If you're pulling in next to mine and after parking there's a thud and a ding in my door it's likely going to be you who did it.

I do get the idea of having it record for 20 min's after shut-down, but I really don't need 20 minutes every time I pull into the garage. I think I'd rather have it shut off when I turn the truck off. If I want to record what goes on when I'm not present I like the idea of triggering the device and having it remain active until I step on the brake pedal. With the engine running or not - the brake pedal will stop the recording. If I forget - that's my issue. After all, it isn't like my truck gets hit all the time. So this is a passing interest. And I really haven't started construction on it because I'm working on plans for a workshop over my garage. Space may also double as an exercise room for my wife and her hot friends. I could set up a security camera and record anytime it detects motion.

I wonder how much current that security system I have in the closet draws. Maybe I could set that up as a dash cam. Only problems with that is it doesn't record speed or location, and when the truck is parked, if powered down it might not keep the time and date setting. It should, so maybe that's something I can play with.

In the end, it's all for fun. Nothing I find myself in dire need of.
 

PadMasterson

Joined Jan 19, 2021
29
Tonyr1084, I understand what you are wanting to do and I get that you're not a target all the time. :) Like I said, I have a power adapter plug that has an LED and switch built in and I power my Dash CAM with that. I just switch it off when I pull in the garage and turn it on as I pull out. The 20 minutes thing is just a nice built in way of recording when I park some place for less than the timeout time. One thing I will say, I found that on my 2019 Ranger, the stoplights and turning lights have what I believe is a short circuit detector circuit built in. I was trying to connect up one of those LED strips that I've seen under the tail gate and it got all kinds of confused when I connected it. After looking at the signals with a scope, I found that there is a 200uS pulse every 4.5 mS on the lines. These pulses went from the 12V level to about 2.4V. I think, but could never find a real answer, that these are used to detect a short or the addition of a trailer light connection even with a switch that tells the system I connected one, if I did. I sent the light back and haven't went down that road since. (No pun intended.) If you connect anything to your stop light circuit, you may need to check if it will cause any other issues before leaving the driveway. Just saying... :) Good Luck... ;-)
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,270
After having been reminded to tinker with this - and the goal was to replace the relay with transistors I've come up with this. Please - anyone - everyone, review my logic and tell me if I missed something.
1611272345786.png1611272370597.png
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,270
sghioto I see Q1 and Q2 but I don't see Q3 in your circuit. Also, my R2 & R4 are 100K, not 10K. Later today I'll give it a shot on LTSpice and see what I come up with. The intent of Q1 is to be on when the key is on. Q1 should stay on when Q3 is activated. Q3 is activated when Q2 is momentarily activated. The activating of Q3 also keeps Q2 active until the brake pedal is pressed. Since Q3 is PNP it is held to ground via (in my diagram) a 10KΩ resistor in series with a single standard incandescent 35 watt brake light bulb. That should be enough to keep Q3 on once Q2 has supplied a brief period of voltage. D2 should keep Q1 active after the key has been turned off. To keep Q3 active, it keeps Q2 active, which (in theory in my mind) should keep the system on. D3 is necessary to keep Q2 active when Q3 is active, and Q3 relies on Q2 being active to keep it active. IN THEORY!

[edit] oh, wait - your circuit is meant to be different. OK, I'm looking at it.
 
Last edited:

sghioto

Joined Dec 31, 2017
2,395
The issue in your circuit is D2 and D3. They are both reversed biased when SW3 is pressed. The collector voltage on Q3 is lower then the voltage on the cathodes.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,270
Been messing with LT Spice. Yes, my circuit did not work the way I thought it would. So I spiced your circuit (sghioto) and the sim isn't working as expected either. Have a look:
V1 is IGNITION. (delay 1 sec to ON, 10 sec to OFF)
V2 is 12V (B+ always hot)
V3 is Brake Lights (delayed 15 sec) (to shut off)
V4 controls SW1
 

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Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,270
sghioto no, I'm not 100% sure, but I think I got it right. That's why I posted the ASC file so others can run the sim and see what I'm seeing. Logically, your circuit looks correct; so . . .
 

sghioto

Joined Dec 31, 2017
2,395
I was able to use an online simulator called Multisim which sorta worked as well. With the component values listed the LED would be ON when first starting the sim unless either I removed C1, or if I leave C1 in and changed R1 to equal R2 it worked as expected.
Since I did not have a premium account I wasn't able to define Q1 and Q2 to a specific part #. That may explain the anomaly.
What is V1 through V4 suppose to indicate on your sim
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,270
V1 sim's the ignition key
V2 is the car battery
V3 sim's the brake light
and
V4 controls S1.

I'm learning how to use the switches. I could replace V3 with a switch and make a battery node, but this was less work for my brain.
 
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