Switching 12v

Forum 2005-2010 (read only) Hardware Interfacing
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As the title suggests, I am looking for a method to apply +12v to a device. Normally I would use a transistor with the load on the collector, however, this application has a few restrictions.

Basically, I need to control every item in a gauge cluster from a car. I do not wish to pull it apart and modify it - this will impeed on future serviceability. It has a common ground wire, and an individual supply line for each indicator. I understand I could use these backwards, and make the ground a common supply instead, but, the tachometer, fuel, and temp gauges use the common line as well - and as stated, i do not wish to modify the cluster to account for that. I could also use a relay, but the ammount of space 20-30 relays will consume is not permissable.

Any Ideas?

Thanks in advance.

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What kinds of currents are you talking about switching here? You can use transistors configured as load switches to do the job, but the details depends on the switching current.

The circuit here (the one at the bottom) was designed to switch a 3.3V load on and off, but if you eliminate the LD1117 you are basically switching 12V to the load on and off. The NDP6020P shown in the schematic can handle pretty big currents; I'd say you're safe up to about 4A.

You'd have to replicate the 2 transistors+3 resistors for each instrument in the cluster that you want to switch.

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Thank you for the replies. I have never hered of "opto-coupled" transistors, and will definately look into this more.

The max current per switch (at an educated guess) will be 2A. Typically I wouldn't expect most to be more than 0.6A from my breif sampling measurements prior to disassembly - although I was more concerned with interperating the gauge signals at that stage.

The 2 transistor + 3 resistor method apppears to be an accessible option; I understand I will need to replicate this a number of times.

Thankyou for steering me in the right direction - I appreciate your time.

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You can use a relay.

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As stated originally; I do not wish to use a relay. The main concern is the ammount of space each relay and supporting components will consume. Then there is the horrid sound with each click (console indicators change frequently...). Plus the higher likelyhood of failure... And the cost. Thanks anyway Casey :slight_smile:

I will be using relays to accomplish results elsewhere in the vehicle (External Lights, Fuel Pump, Headlight Motors, Sunroof Motor, etc, but not with respect to the gauge cluster, and in locations where servicability is maximised.

For anyone interested; I am overhauling a honda prelude 3rd gen. Basically - to improve my knowledge on how the vehicle works and familiarise myself with its idiosyncratic design and automotive concepts. I am doing as much as i can myself - from rebuilding the engine, to body work. I intend on using arduino's in my prototype to control each locality of components, and interconnect them with a bus system. This will interface via serial with a computer for simplicity of GUI implementation for control, calibration, data logging, time trials, service history, and to an extent - remote control and monitoring. I have investigated a number of bus systems including ethernet, MIL-1553, IIC, CAN, and Profi. For simplicity sake and the cost, I will most likely use Arduino's in my prototype with IIC. Although there is a bit of gray area regarding it's maximum bus distance, I have tested it with 4 devices in a star topology with 5 metre legs successfully using cat5e utp, which is much larger than it will need to be in my car. To date; I have aquired 2 cars. One is completely stripped, the body disposed of, and components disassembled (except the engine and gearbox) bagged and tagged... The second is still complete, with the exception of the gearbox which failed on a leasurley drive and is in peices awaiting parts. As i re-assemble each compoent from the first car, I am drawing schematics of what each assembly contains, which i will then use to determine a control measure.

I am rather new here as you can tell from my post count. My name is Gui, I live on the Mornington Peninsula (VIC) Australia, I am 20 years old (almost 21), and work for an engineering company which specialises in a helicopter recovery system subcontracting to the defence force. I have always had an interest in electronics, but i guess up untill now i have found good education hard to come by. Quite often at school the teachers understanding of simple concepts in science, IT, and 'systems' was below mine, which says a lot about them. What i like about arduino is how simple it makes it to perform otherwise complex tasks (in my opinion) at a low cost with little eduction; which consequentually forces me to learn more. I hope to one day study engineering at a deeper level with a major in mechatronics, but before commencing higher education I wish to complete an electrical apprenticeship. As much as engineering interests me personally, I find laboursome work more fun, and would enjoy the perks of an A grade license. I was always a nerd at school; no friends, math was my best subject, and i spent most of my time learning web programming languages, and dippen my feet in C# and C++ every now and then.

I hope eventually to be in a position where I can return something to this community rather than consume everyone's time with simple questions. I do try to find answers myself, and do try to make the most of the search function available in this forum; there are times when all I find goes straight over my head.

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If you don't already have one, you probably need to get a Honda factory service manual for the year and model of the car you are going to rebuild.

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If you don't already have one, you probably need to get a Honda factory service manual for the year and model of the car you are going to rebuild.

I have a Haynes one, which is quite comprahensive. Although I am not getting anything out of it I don't already know or can't figure out. With the ammount of work I am doing, it will be of no use at all during re-assembly. The electrical system is obviously going to be completley different. I am investigating different ecu's, mainly Hondata for engine control. Routing the vaccume system, cooling system, and engine electrics will need to be different, with a minimalist focus, and air conditioning is definately on the way out. A lot of the mounting hardware will be different to account for this.

The illustrated parts break-downs are good, but i don't really need a 30 step procedure to remove some bolts and washers. I guess what I really need is in depth generic information on how to do things like balence the crank shaft to account for thicker rods and aftermarket pistons, or set up to hone the cylinders - which I am slowly obtaining from other sources. :slight_smile: