CHEAP Wideband kits!

L6 and Bort62, I hear ya both, I'm looking around here for somebody who likes that smell of solder in the morning as much as I like the aroma of 80-90W gearlube - hopefully I can find somebody willing to swap projects with me.

Harte3, from what I can tell, once I get everything electronic hooked together (JAW, MSD, Gauge of some sort), it'll all hook up to just about any car via simple 12V and ground leads (plus welding an O2 sensor bung to the exhaust).
 
Bort62":1en8j5b0 said:
Trivial to do, for someone who knows what they are doing (like me).

If you aren't familiar with electronics, it will be a steep learning curve. I am perfectly willing to coach you on how to do it however.
Click to expand...
OK, I went to my local electronics store, and I/we need some coaching. (It's a small store)

On the Tach Input's voltage divider:
* Why not just use an "Integrated Circuit 3-terminal Positive Voltage Regulator", like an NTE960 (replaces ECG960, SK3591)? It's specs are: Vin - 35V Max, PD - 15W, Io - 1A, Vo - 5V. It'd require a heatsink, but since there's already one on the JAW...
* Is the item in the voltage divider schematic above between the 1k and 39k resistors a diode? We're assuming so, but wanted to confirm.

On the output (gauge) side:
Got any suggestions on which step-up regulator and op amp to use? We spent awhile looking through parts books, and the guys were hesitant to sell me parts without knowing more info about the JAW. Part numbers would be extremely helpful.
 
jamyers":2pdsa9no said:
* Is the item in the voltage divider schematic above between the 1k and 39k resistors a diode? We're assuming so, but wanted to confirm.
Click to expand...


Yes it is a diode, but I believe that is a zener diode. Your electronics guy should know the difference.
 
Okay, here's the deal.

If your tach output is a square wave with an amplitude of 12v and an offset of 0 volts (simplifying assumtion), and your input on your device takes a 0-5v input. then use a 5v zener clamping diode to clamp your tach output to an amplitude of 5v.

A zener diode is like a releif valve. Anything over its value it "vents" (shorts to ground) so you put 12v up to it, you will get it's value after it.

This should work, and is by far the easiest solution.

What he's got there is a 9v zener diode. He is clamping it to 9v and then dividing it down with the divider. The 1kohm resister upstream limits the current that can flow through the diode to prevent it from burning up. Probably a good idea.

The voltage divider he is using will lower the voltage by a specified ratio. There is also a capacitor there which acts as a filter to pull out high frequency noise.

The circuit he has will certainly work, but it could be simplified for this particular application (I think) to utilize just a current limiting resistor, a 5v zener, and a filter cap.


Now, for the gauge, you can buy DC-DC converters that have a 12v input and a 24v output. Utilize one of those with an op-amp like suggested to scale your input voltage for your gauge.

An op amp has a gain (which is set by resisters) and it will multiply the input voltage by that gain to get the output voltage (assuming the output isn't higher than the rail - which is the 24v you put into it).

As for part #'s, any op amp will work. There are about a million different part #s out there so it's hard for me to suggest something that you will actually have available at your local place.

Just get a single channel op amp. and you should be in business. Once you have it, look up it's data sheet online and copy the non inverting circuit for it. It will use a couple of resisters to setup the gain.

As for the DC-DC converter, look on digikey. They are all over the place.
 
Thanks for the info, I'll be doing some reading tonight. :D

I searched digikey for 12V-in dc-dc converters, and the biggest thing listed was 15V output. If I broadened the search, I kept getting the TI PT5040 series step-up regulators, which spec for 4.75 ~ 14VDC input and up to 20VDC output. The spec sheet indicates it's intended for 5V inputs, but would it work? (then again it looks like that part is $15 each, which kinda defeats the whole 'inexpensive' purpose of this exercise...)

I see what you mean by steep learning curve. :LOL:
 
OK, I went by RadioSnack and picked up the parts to make the voltage divider, using a 5.1 Zener diode and a small (1K/47K) voltage divider to get down to 4.99 volts, just under the 5V max input.

On the output gauge side, my brain hurts. Correct me if I'm wrong, but since I need to go overall from a signal voltage range of 0-5 to a range of 8-18V, that works out to 2X + 8, where X = the gauge signal voltage. Using that equation, 0Vinput = 8Voutput, 1Vin = 10Vout, 2Vin = 12Vout, etc. So wouldn't I actually need an op-amp to double the 0-5V signal, then a dc-dc converter or step-up regulator to add in an additional 8V? (like I said, my brain hurts at the moment)

Anyways, still no luck in positively identifying a "step-up regulator" or a "dc-dc converter" that will work, but they've got a 741 OpAmp with the same 8-pin layout as the one on the playinghookey website.

Couple of questions:
* OK, so I'm going to have to use some external resistors to set the opamp gain - any idea which ones to use to get the above 2X+8 gain?
* On the playingkookey website, the opamp experiment page makes sense (after reading and re-reading), only it's not clear what is going into the chip at pin #7 (V+ on my schematic). Any idea?
* In my case, I'm assuming that the V+ going into the opamp would be the 18 (or 24) volt output from the dc-dc converter, am I right?
 
Before investing any more time and money have you tested the gauge to make sure it is suitable? There is a high likelihood it will not function in they way you are hoping and you will be wild as a hornet if after sorting through the electronics you discover it was never going to work from the start.

To answer a couple of your questions.

The gauge requires 18V for full-scale reading; the JAW unit has 5V output so you require an amplifier to boost signal voltage.

The amp must capable of providing an output voltage of at least 18V at sufficient current to drive the gauge. (The 741 has a current limit of 25mA which is likely to be borderline for an automotive gauge so you should choose something fatter.)

The maximum output voltage an amplifier can produce is (typically) a few volts less than the amp supply voltage. Or to put this the other way around; the supply voltage to the amp must be at least a few volts higher than the largest output voltage expected from the amp.

This means the supply to the amp must at least 22V, say 24V.

The vehicle supply is a nominal 12V, so you require a dc-dc converter to generate the 24V required by the amp from the vehicle supply.

There are numerous IC to do this, the following is an example.
http://www.st.com/stonline/books/pdf/docs/5257.pdf

The most difficult part of this exercise is mounting the individual components, as you are unlikely to have the facilities to cut a custom circuit board.

You would save yourself hours of time by purchasing these items as kits complete with circuit board and assembly instructions. Generally the kits are not much more expensive than purchasing the individual components and you get everything required in a single visit to the store, even so by the time you buy the electronic parts, a case to hold them, some gas to and from the store you will not have much change from the $80 you saved by not buying the special purpose gauge.
 
L6":pd0jhxsm said:
Before investing any more time and money have you tested the gauge to make sure it is suitable? There is a high likelihood it will not function in they way you are hoping and you will be wild as a hornet if after sorting through the electronics you discover it was never going to work from the start.
Click to expand...
You're right, I'm starting to have my doubts about this idea... How would I test it? It's 8-18V meter, drawing less than 100mA. The 0-5V signal is linear, straight voltage output for sensing.

L6":pd0jhxsm said:
You would save yourself hours of time by purchasing these items as kits complete with circuit board and assembly instructions. Generally the kits are not much more expensive than purchasing the individual components and you get everything required in a single visit to the store, even so by the time you buy the electronic parts, a case to hold them, some gas to and from the store you will not have much change from the $80 you saved by not buying the special purpose gauge.
Click to expand...
Thanks for the link, that and your comments clears up a lot of things for me.

It's funny how like the guys above said, it's a different language. Guys would tell me I just needed a converter and an op-amp, and I'm thinking I just need to go buy two little electronic gizmo's and hook them together. I think it was yesterday that I finally clued in that we're talking a board with whole bunch of electronic gizmos on it - two sets of gizmo's, actually. :(
(although I do think that us mechanical-types are better at explaining our stuff than most of the electronics-types I've met recently elsewhere).

Anyways, where could I find one of these kits? I have NOTHING locally, and as you might have guessed I'm over my head looking at most online elec stores.

I may have to just suck it up, get in line and shell out the bucks for a ready-made gauge.
 
Well, honestly - I do know how to do all the stuff you are trying to do and I would probably just buy the gauge.

I don't think your 8-18v gauge is doing to do what you want anyways.

You can buy a 0-5 volt meter pretty cheap from digikey I believe
 
You can get the AEM brand UEGO sensor and gauge on ebay for about $225 delivered. I have it now, but have not installed yet. Hopefully I can tune lean-of-peak and get a little better than the 13 MPG I'm presently getting...
 
Well, after much digging, reading, head-scratching, and a couple of beers... I ordered an assembled JAW with the digital display for $100, plus the sensor off of Amazon for $43. I'll worry about where to put the display when it gets here. I've got the parts from RadioShack to put together a voltage divider so I can datalog the RPM output from my MSD box, and to heck with my gauge idea. Next, I'm heading to my favorite wrecking yard for a GM MAP sensor and a TPS, and I oughta be able to tune my boat to within a fraction of an inch of its life.

All for well under $200, probably $160 or so.
(and if I decide I *need* a gauge, I can get an Innovate G2 or G3 gauge for $65 and be done with it.)

Thanks everybody for the input, it's a learning experience! I'll keep everybody posted once it all arrives. :D
 
Next question for you electronics wizards:

Along with the JAW, I'm also planning on adding a TPS and MAP sensor.

To get a good 5v supply for the sensor's reference signals, which would be better, a voltage divider or an integrated circuit voltage regulator?
(like the NTE960 I have on my desk: Vin=35v max, Vout=5v, Pd=15W, Io=1A.)
I'm thinking the regulator, but then a voltage divider wouldn't need a heatsink.....

Any idea how much load a basic GM tps and map sensor draw, would one regulator be sufficient for both sensors?
 
Regulator.

The divider output will fluctuate with bus voltage, which will change when you do things like turn on your lights. (or at idle vs speed)

Neither the MAP or the TPS should draw much. I am sure a single regulator would be fine.

What's it's rating? 1A ?
 
Haha, well -

That's the precise question I spent 7 years in college trying to figure out (only supposed to be 4).

I don't know :) You could probably get away with up to 1/4 amp.

Just attach it to something metal on the car somewhere - there's your heatsink.
 
Bort62":336yh1is said:
Haha, well -

That's the precise question I spent 7 years in college trying to figure out (only supposed to be 4).

I don't know :) You could probably get away with up to 1/4 amp.

Just attach it to something metal on the car somewhere - there's your heatsink.
Click to expand...
I lknow what you mean - 10 years of college down the drain, lol.

I stopped by RadioSnack and snagged a heatsink for $1.59, after having to explain it to every employee in the place (sigh). They kept showing me heatshrink, even after I explained what one does. Go figure - I may not know beans about electronics, but I know more then they do, if that's supposed to make me feel better. :roll: :D
 
You must log in or register to reply here.
Back
Top