Autosport Labs

Hi guys, need a recommendation on a non MegaJolt project from someone who knows something about electronics. I'm a guy who can solder and follow directions but doesn't know much about electronics except the "don't let the magic smoke out" rule. I'm building an air/fuel ratio gauge and the plans call for a 2.3k and 3.3k resistor. Any recommendations? Tolerence, watts, etc.? Part numbers and suppliers would be a great help. I did make a go of it on my own, but I'm just not sure what would be best. Any help would be appreciated.

On topic my MJLJ sits completed waiting for the car to get complete enough to be installed and tested.

Thanks, Jack

Well the plans should really say what tolerance and wattage to use rather than you, as the constructor, having to work out what to use!

Are you able to describe what part of the circuit they are in and/or what they do...or post the schematic?

*Probably* 0.25watt, 5% will do (buy them at anywhere that sells resistors, eg Maplins), but a quick once over of the schematic is the right thing to do

Thanks for the reply Martin. This is what I'm working from (schematic is here too):

http://www.scirocco.org/tech/misc/afgauge/af.html

I stopped in at my local Radio Shack that's going out of business during lunch today. They had 3.3k, 1/4 & 1/2watt, 5% tolerence but not 2.3k. They had 2.2k. Since everything was on clearance I went ahead and got the 1/4 watt of each, 1/2 watt seemed too big based on the MJLJ components. If you check the schematic, can you tell if using 2.2k instead of the 2.3k would make a big diffence? The circuitry is pretty simple compared to the MJLJ stuff so I'd appreciate your opinion if you have time.

I know you can buy an A/F gauge for about $30 now but I like the idea of building it since, well, I can! Plus the ones on the market are ugly. I can take this and build it in a nice custom housing.

Thanks again,
Jack

Ah, the venerable LM3914N.. Interesting little project!

OK...

Wattage is not important here - 1/4W or so is fine. From reading the web page, it seems that the operation and setup of the meter would benefit from them being adjustable - so that takes tolerance out of the equation completely!

So I'd put in 4.7K or 10K potentiometers so that they can be adjusted as required.

If you're buying in the UK, then I would be going for something like these...
http://www.maplin.co.uk/Search.aspx?cri ... 3D&DOY=6m5

PS I hope your soldering comes out better than that shown - that really is atrocious!!! Mainly because those blue wires are far, far thicker than required - each one wouldn't be out of place on a headlamp circuit...

Something of a misnomer when labeled for A/F monotoring. Just a voltmeter for reading a narrow band O2 sensor. Such sensors only read accurate at stoic, anything else is simply above or below without any relevant scale. You will have a light show but no worthwhile information as non-stoic reading are just used by an ecu to bump toward stoic in closed loop operation such as low power and idle. Of no value for tuning. Google on wide band O2 for more information if you are looking for something that can be used for tuning.

Thanks for your comments Martin. I'll check into using the potentiometers instead. Any comment on what affect using a 2.2k resistor in place of the 2.3k would have? And yes my soldering is much better than that on the site.

Jack

...Any comment on what affect using a 2.2k resistor in place of the 2.3k would have?...

Using a potentiometer for this resistor means that you can adjust the brightness/calibration (can't remember which one) to "as required", so it doesn't really matter what the final resistance is compared with the 2.2k circuit design

(...just wire the pot in place of the resistor using one end of the track and the wiper as the two connections)