# Anyone interested in a small project? \$

#### jip911

Joined Feb 18, 2013
7
Hello,
First off let me state right off the bat my electronics experience in limited at best, (I struggle to program the clock on the microwave.) Having said that, I am looking for some help building a little project. I am willing to pay for someone to write the programming and even build this simple circuit.

Anyways heres the details of the project.
I have a Side by Side ATV that does not come equipped with reverse lights and I would like to add some to the unit. I could add a limit switch to the gear shifter, but I would rather tap into the signal that comes from the gearbox positioning sensor (GBPS) that runs to the dash display and changes the gear position display from P (park) R (reverse) N (Neutral) etc.

With my limited knowledge of micro-controllers, I believe this can be achieved with a micro-controller and mosfet. The signal from the GBPS is 1.4v  1.8V when the transmission is in reverse. The signal that enters into the GBPS before being knocked down is 5v so I imagine I can tie into it before it enters the GBPS to grab power for the controller/mosfet

I have a pic of a circuit that someone else put together but no other details

Am I on the right track here? Does my summary make sense? Basically if the controller receives a voltage between 1.4v-1.8v supply voltage to the mosfet, so that it opens. Then I will have one terminal go to ground and the other go to the lights ground

Anyone interested in either building this circuit or supplying the code for the chip and I will buy a programmer.

#### WBahn

Joined Mar 31, 2012
30,290
What are the voltages coming from the GBPS for the other gear selections?

#### jip911

Joined Feb 18, 2013
7
P = 1.0v
R = 1.8v
N = 2.6v
H = 3.4v
L = 4.4v

Does my explanation make sense? Is there another way I should approach this?

Joined Apr 30, 2011
1,581
You seem to have clean 0.8V steps (except the last one) so a window comparator set for 1.6V through 2.0V might work well.

#### jip911

Joined Feb 18, 2013
7
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#### WBahn

Joined Mar 31, 2012
30,290
I haven't looked at the SparkFun window comparator specifically, but something like that will probably work fine for you and if you don't want to get too involved with the electronics then it is quite possibly a very good route for you.

One thing to watch out for, though, is that automotive environments are notoriously harsh on electronics. Your ATV probably isn't as bad as most cars, but it might even be worse just because cars are specifically designed to address it and your ATV probably isn't.

If you are somewhat interested in the electronics, an alternative for such a simple task as this is just a simple one-transistor comparator in place of each comparator in the schematic followed by similar switching logic afterward. Or you could even run the light between the two so that one has to be high and the other has to be low in order for it to light. A number of different ways to do it.

#### jip911

Joined Feb 18, 2013
7
Thanks Wbahn for your comments, I think I will order one of these and see what it does. Looking at the schematic, I might as well be trying to read Chinese as my electronics knowledge is very limited.

I still dont understand exactly how to wire this thing nor what signal it will produce if I do get it set up correctly. Then I have to figure out what to do with that signal in order to get it to run these lights.

Thank you for taking the time to respond!

J

#### thatoneguy

Joined Feb 19, 2009
6,359
Use a 7805 Voltage regulator to power that circuit and Piezo buzzer.. Put a 10 ohm resistor in series with the 12V side of the 7805 Vin, along with a 220uF 35V capacitor on the input side of the 7805. The resistor will limit peak voltages/surges, and the capacitor will help smooth out noise. On the output of the 7805, use a 22uF cap and power the board from there.

Does that description make sense? Make sure you get automotive rated capacitors, they have a wider temp range and are less affected by vibration as well. Digi-Key or mouser have "Automotive" categories for components. The rest should be mounted in a project box with a bit of cushion so the solder/traces on the SparkFun board doesn't get vibrated/shock cracks. A grommet mount (use 2 grommets like washers on each side of box when bolting in place) is good damping, but try to find a location that doesn't vibrate to mount it.

Make sure you use a low temp (25-35W, 300ºC max) soldering iron and Rosin core solder (Radio Shack has both). There's been a few circuits like this where plumbing solder/acid core was used with a soldering gun, and that doesn't work. Spend the extra money if you want it to work at all, and last more than a week.

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#### jip911

Joined Feb 18, 2013
7
Your explanation makes perfect sense to me on how to regulate the supply voltage to the board. I will order those items mentioned, now I am still confused on how to wire the logic, vref high, and vref low on the board. Can anyone help me here?
I really appreciate the responses given!!

J

#### thatoneguy

Joined Feb 19, 2009
6,359
The Sparkfun Board linked above had 2 potentiometers already on it to set the voltages, so it would be connect it, put in forward, adjust until buzzer goes off, put in reverse, adjust so buzzer is on. There should be a datasheet with it that explains which pot is high and which is low for the "window".

Once it is set, put a dab of hot glue on the pots as well as on the IC to help prevent vibration damage, it keeps all parts moving at same speed, so fewer breaks. Hot Glue can be peeled off later if you need to re-adjust. Just dabs are needed, no need to put a 1/4" layer across the board.

#### jip911

Joined Feb 18, 2013
7
Sorry for all the stupid questions but I am "not getting it" so to speak... There are 3 connections on the board for logic, vref low, and vref high, I'm assuming that when the voltage is in the window set by the pots it puts a current out on the logic terminal that I would then run into the gate on a MOSFET then hook the drain to the negative of the lights and the source to ground. What voltage would I expect on the logic wire? And would there be anything hooked up to the vref high and low terminals?

Thanks again for your input !

J

#### thatoneguy

Joined Feb 19, 2009
6,359
The pins on the board for vref lo/hi are for an external reference. By default, the references are set by the potentiometers.

The output of the 7805 + would go to Vcc, The ground of 7805 and board would be tied to chassis ground, the signal in would be the voltage from the shift sensor, and Logic Out will be either High (5v) or Low (0V). The Logic Out will be High (STAT LED on) when Signal In is Higher than Vref-low, and Lower than Vref-High. LOGIC will be LOW/0V (STAT LED off) when input signal is higher than Vref-high, or lower than Vref-low.

Does my summary make sense? Basically if the controller receives a voltage between 1.4v-1.8v supply voltage to the mosfet, so that it opens. Then I will have one terminal go to ground and the other go to the lights ground
Set Vref-High to 1.8V, and Vref-Low to 1.4V (center pin of each Pot), the pots are each set up as a voltage divider for 0-5V.

When the voltage is between 1.4 and 1.8V, the LOGIC output will be 5V, which can NOT source much current, so you'll need to follow it with a switching transistor to power the 12V relay coil, which will power the backup lights and buzzer. This can be added to the piece of stripboard that you use to mount the 7805 and caps, since you'll have both the 12V signal there, as well as ground. Just be sure that the LOGIC out is separated from the 12V in.

Connection would be similar from the logic line to the STAT LED, except where the LED is, you'd add your relay coil, and a MOSFET rather than a BJT. Use the logic HIGH out to switch a MOSFET which switches the relay ground side, rather than a BJT.

Let me know if you'd like a schematic/simulation of this drawn up and posted.

#### thatoneguy

Joined Feb 19, 2009
6,359

Otherwise, the blue trace is the LOGIC input from the comparator (Simulated with a source in schematic), and the green trace is the current through the "relay" contacts, indicating relay is enabled.

I left out the Voltage regulator portion, but it would be on the same board, supplying the 12V (on the right side in schematic), tapped prior to the resistor on the 7805 input.

You don't see a 12V on the simulation output, since I'm showing current through R1 and coil of relay so they match and the scaling isn't confusing.

R2 is REQUIRED, otherwise MOSFET will not shut off when signal goes away.

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