It has been some time now since I last participated in this forum. Other things have caught my attention and I haven't had any electrical/electronic projects. However, now I could sure use assistance. The project I am working on most probably has a simple solution but I'm not an EE boy, just an individual who can build most anything if given direction.
Please refer to the attached picture:
From the picture I think it is pretty self-evident what I am trying to do and what I need. I need a + 12V feed activated by the engine oil pressure switch. Since it ties into one of the vehicles computers it would be safest if the hour meter was also completely isolated from the circuit. I would like to keep it as simple as possible and also if possible solid-state. I can picture how to do it with a mechanical relay but I'm having difficulty figuring out a solid-state solution that would isolate the hour meter and not cause any problems with the computer.
Your assistance as always, is greatly appreciated.

 

https://www.farnell.com/datasheets/1448938.pdf

The 12v model of something like this should work.

 

Thanks for your rapid response.
I sent a inquiry to Curtis for the proper application.
They seem to be oriented around commercial accounts and I hope they respond
Looks pretty fancy, hope it not too expensive.

 

Thanks for your rapid response.
I sent a inquiry to Curtis for the proper application.
They seem to be oriented around commercial accounts and I hope they respond
Looks pretty fancy, hope it not too expensive.

Those are the cheaper ones. The fancy omron versions are in the hundreds each.

 

So, to be clear, you want to count time when the oil pressure switch is open (ie engine running).

Those Curtis ones are about £25 One issue is that cars are not 12v; they are 10 - 14v and very spikey.. Looks like model 700PN14J would be the best option. You still need to invert the logic so when the switch is closed no power goes to the hour meter (or its not enabled).

Some simple solutions:
Option 1: As you suggested, a 12v relay, connected from a suitable B+ feed to the switch. The relay contacts then power the hour-meter. But, as you point out, there may be issues with this.
Option 2: Use the relay as #1 but use a transistor to drive it. Here I use a 8v zener and an optocoupler ensure that the switch is isolated and the ECU won't see any reverse current. This option could drive the meter directly as shown further below.

 

Can't you simply operate the meter off the ignition switch? The time for which the ignition is on but the oil pressure is zero is likely to be insignificant compared to the time for which the engine is running.

 

Here's a example of a DC output SSR which should work, if you really need a relay.

 

FWIW, my hour meter is powered by a small battery that lasts for years. It only advances when it sees pulses in one of the spark plug wires. It has a wire you wrap a few times around the plug wire. It was less than $10

 

FWIW, my hour meter is powered by a small battery that lasts for years. It only advances when it sees pulses in one of the spark plug wires. It has a wire you wrap a few times around the plug wire. It was less than $10

Are you gonna keep the model secret?

 

Something like this: https://www.aliexpress.com/item/1005007227320209.html



Records the number of hours it 'sees sparks'

 

Interesting device, that counter.
However, all of my vehicles, model years 2014 and 2021, already have coil-on-plug ignition, and I suspect all modern vehicles will be the same.
As such, it won’t work and an oil pressure switch as originally proposed would be the required alternative.
Or an even better option, is to tap from a switched outlet as suggested by Alec.

 

Are you gonna keep the model secret?

Mine is an old yellow Briggs and Stratton 5081. Looks like you need a time machine to get one now. There are similar devices still available.

https://www.amazon.com/Briggs-Stratton-Maintenance-Minder-5081K/dp/B0012W3V4C

 

Mine is an old yellow Briggs and Stratton 5081. Looks like you need a time machine to get one now. There are similar devices still available.

https://www.amazon.com/Briggs-Stratton-Maintenance-Minder-5081K/dp/B0012W3V4C

One new on eBay https://www.ebay.com/p/1900685620 at a stupid price!

Or buy a stupidly priced equivalent: https://www.tractorsupply.com/tsc/p...ines-replaces-briggs-stratton-oem-5081h-5081k

 

Or buy a stupidly priced equivalent: ...

That's crazy. I suppose they know what they're doing with their pricing but they're limiting their market to just a few people that really want/need it. Mine is on my boat engine and I doubt I would have installed such a pricey one.

 

FWIW, same function and under $10

https://www.amazon.com/gp/product/B0CKQN11FW

 

You are all amazing with your willingness to help out a neophyte like me. I'm really not new to this but my knowledge lies somewhere between electrical and electronics. I am old enough to remember when Ham radio operators still built their own equipment. To me that was the fun part. I've built receivers, transmitters and antennas with only a rudimentary knowledge of how they worked.
Irving, Yes, the oil pressure switch is NC. My guess is that it is kind of a fail-safe. No oil pressure - switch closed light on. But now that I think about it I guess the switch could fail open also. You are right I need to count the time that the switch is open, and the engine is running.
Alec_t The vehicle I am working on is a hybrid and the engine is not always running when there's an ignition feed. That would make it altogether too simple. The engine time versus ignition time is not the same.
Crutschow I am having difficulty figuring out how to wire an SSR into a circuit which needs to provide an ignition feed to the hour meter when the oil pressure switch is open and when it is closed it is to ground.
I am also concerned about freaking out the ECU.
wayneh There are no spark plug wires. Them were the old days.
Irving Thanks for the suggestion but you know that would be just too simple. As schmitt trigger pointed out my car has coil on plug ignition and no plug wires.

So, Irving it appears as though you have the most viable solution at this point. I have been studying the two proposed schematics that you sent. I understand most of the first one, but I am confused over the hour meter shown in the second one. I could build this project on a little breadboard and then enclose it in epoxy if none of the components generate heat. Then place it directly behind or close to the hour meter. Then all I would have to do is fine the best place to tap into that little yellow wire.
1. Would B+ be an ignition feed?
2. What is U1, PC817A
a. Can this be purchased from Digikey?
3. Q1, 2N3906 2N3906 BZX84C8v21 PC817A 1N4148
a. Are these the numbers I would use to order theses parts?
4. Will Digikey sell individual parts is such small quantities?
a. If not does anyone have a suggestion as to where I might purchase these parts.

 

The vehicle I am working on is a hybrid and the engine is not always running when there's an ignition feed.

How do they stop the engine if not by cutting the ignition voltage and/or power to the fuel-injection system?
You should be able to tap into one of those voltages.

Edit: It likely stops the engine by cutting the fuel-injection power.
That voltage may come from the fuse box.

 

There are 13 separate and different ECUs (computers) in this car. They all communicate between each other and make thing happen via a CAN Bus in ways that sometimes is only in the mind of god.
Gone for ever are the days of a switch, a wire and a load.
Example: A capacitor on the instrument panel display went out and the tail gate would not open, the engine would not shut down......... A couple of days learning and diagnosing. A 50 cent part and another day dismantling the entire dash made everything better.
What you are suggesting maybe possible but it also could turn into a disastrous, expensive mess.
I was headed down the road that I thought didn't require being a Toyota electrical engineer.

 

So, Irving it appears as though you have the most viable solution at this point. I have been studying the two proposed schematics that you sent. I understand most of the first one, but I am confused over the hour meter shown in the second one. I could build this project on a little breadboard and then enclose it in epoxy if none of the components generate heat. Then place it directly behind or close to the hour meter. Then all I would have to do is fine the best place to tap into that little yellow wire.

1. Would B+ be an ignition feed? Yes
2. What is U1, PC817A Its an optocoupler;
a. Can this be purchased from Digikey? Yes
3. Q1, 2N3906 2N3906 BZX84C8v21 PC817A 1N4148
a. Are these the numbers I would use to order theses parts? Yes, or use generic descriptions eg BZX84C8v2 = 8.2v 500mW Zener diode, see below
4. Will Digikey sell individual parts is such small quantities? Yes, see BOM below, shipping is main cost as always.
a. If not does anyone have a suggestion as to where I might purchase these parts. eBay, local electronics store, Mouser, other online retailers. I'm in UK so can't advise on local options

Index	Quantity	Generic Description	Digikey US Part Number	Manufacturer Part Number	Unit Price USD
1	1	DIODE ZENER 8.2V 400MW ALF2	1727-2934-1-ND	BZX79-C8V2,113	$0.10
2	1	2N3906 TRANS PNP 40V 0.2A TO-92	4878-2N3906CT-ND	2N3906	$0.13
3	1	PC817 OPTOISOLATOR 5KV 1CH TRANS 4-DIP	PC817X2NSZ9F-ND	PC817X2NSZ9F	$0.27
4	1	1N4148 DIODE STANDARD 100V 200MA DO35	1N4148FS-ND	1N4148	$0.10
5	1	RESISTOR 10K OHM 5% 1/4W AXIAL	2019-MF1/4LCT52R103JCT-ND	MF1/4LCT52R103J	$0.10
6	1	RESISTOR 390 OHM 5% 1/4W AXIAL	2019-MF1/4LCT52R391JCT-ND	MF1/4LCT52R391J	$0.10
7	1	RESISTOR 1K OHM 5% 1/4W AXIAL	2019-MF1/4LCT52R102JCT-ND	MF1/4LCT52R102J	$0.10
8	1	1FORMC 10A, 250VAC 12v PCB RELAY	39-G6RN-17-E-ASI-CF-HADC12-ND	G6RN-17-E-ASI-CF-HA DC12	$3.36

[edit] I added the relay because I don't know the hour-meter you are going to use. Its more than likely the hour-meter can be driven directly from Q1. Depending on the relay and/or hour-meter we might need to change the value of R2.

 

Irving
Thanks for hanging in there with me. I never expected a complete parts list.

I have attached a file detailing the power meter that I am proposing to use. Typical current draw DC 12V ≈ 10 to 30 mA. Is this the information you need in order to make final adjustments?

As soon as I hear back from you I will get on to the task of ordering all the parts. Looks like this will be a very inexpensive project.

Do you think assembling this on a breadboard would be the best approach.

I could enclose the completed breadboard within a box or encapsulated in epoxy if none of the components generate heat.