Dash sensor modules schematic

[Magnet18]

Eagle scout here, take care of yourself!

[bkahler]

Wayne, hang in there and keep the faith. I'm looking forward to following the rest of this sensor module upgrade once you back and at it again

Brad

[Keyair]

Here is to your health, Cheers!

[WayneG]

A little more progress with this project:
This is the module tester box I made:


It has a 100K 10T pot shared between the fluid sensors and a 100 ohm 10T pot for the fuel level, and a fuel gauge for added glitz
I still need to add labels but as you see it is tied to the dissected module and it is somewhat working.
One thing I am confused about is that the low fuel light comes on at just above 1/2 tank (570 ohms). I dont know if that was the intent or if maybe this module was calibrated for a different sender resistance?
Most GM senders of this age were 90 to 100 ohms at full zero ohms at empty. Newer GM senders used 40 to 250 ohms:

Ford up to 1986 - 73-10 Ohms
Ford 1987 & up - 16-158 Ohms
GM up to 1964 - 0-30 Ohms
GM 1965-1997 - 0-90 Ohms
GM 1998 & up - 40-250 Ohms
Mopar up to 1986 - 73-10 Ohms
AMC 1950-1977 - 73-10 Ohms

I think the low fuel light should come on at about 1/4 tank?
Any thoughts?

[bkahler]

Wayne,

Great progress! As I was going through the instrument cluster building process on my Argosy I found that my fuel sending unit was 90 ohm. Same for the 1986 345 that I used for parts. One thing I didn't find out is whether or not the 0-90 is linear. I'm betting it's not.

I agree the fuel level warning light should come on at 1/4 tank.

Are you planning on making and selling these boards?

Brad

[WayneG]

I know my "original" sender unit was not linear to fuel level. I assume it was so cobed up to fit the depth of the 60 gallon tank.

I could not find a reasonably priced unit so I made my own that has better linearity


The original GM gauge may also be non linear in its readout. The after market one in this tester is 100% linear with 1/4 full =22.5, ohms 1/2 = 45.0, 3/4 = 67.5, and Full = 90 ohms.

As for production, when I get the design fully worked out I will setup to make 8 units, unless there is more demand, that is all I will build.

I suppose a Argosy could be retrofitted to use the fuel level, washer and coolant levels. You would just need indicator lights and a place to mount them.

All of this ambition depends on which direction the doc's are spinning me over the next few months.

[bkahler]

Originally Posted by WayneG

I know my "original" sender unit was not linear to fuel level. I assume it was so cobed up to fit the depth of the 60 gallon tank.

I could not find a reasonably priced unit so I made my own that has better linearity


The original GM gauge may also be non linear in its readout. The after market one in this tester is 100% linear with 1/4 full =22.5, ohms 1/2 = 45.0, 3/4 = 67.5, and Full = 90 ohms.

As for production, when I get the design fully worked out I will setup to make 8 units, unless there is more demand, that is all I will build.

I suppose a Argosy could be retrofitted to use the fuel level, washer and coolant levels. You would just need indicator lights and a place to mount them.

I would be interested in two. I believe the owner of my old 310 would like a working unit and it would be an interesting retrofit for my Argosy.

All of this ambition depends on which direction the doc's are spinning me over the next few months.

Well, let's hope they spin you the right way!

Take care,

Brad

[Keyair]

I have no input on the electronics other than to me amazed, Wayne! Nice job!
Obviously, you can count me in for a unit please!

Hope that whatever is going on with you Health is resolved quickly and positively.

[Waipio Rim]

I am just as amazed as the other Steve. Please sign me up for one.
Steve

[WayneG]

Looking up parts now, so far I have about $300+ for parts. Some are enough to make just 8 units most are bulk order to make many more than 8, like transistors, capacitors, resistors.
I will try and arrive at a price that is just at cost plus shipping.
This is assuming that it does not get to labor intensive and I dont need to hire some of Santa's elves

[bkahler]

I was wondering where the 8 quantity came from, now I understand

[WayneG]

The quantity comes from how many boards I can get out of a 6x9 PC board. 4 on one board. I am upping the parts to make 12 boards (Assuming no failures)
I forgot to add chemicals, with a run like this I dont want to use the chemicals at work. I can still use some gear from work like the exposure light, PC etching tank and mini drill press to save equipment cost.
So far my parts list for 12 boards is about $500, that is about $40 a module for parts. About $9 of the cost can be reduced if I dont use a metal box as an enclosure.
There will be more parts involved as I make some mods to allow for at least the fuel sensor set point to be variable.
It is a work in progress.

[Keyair]

I think that is way cheap for what it is and I bet you will sell all 12 in a snap.
One thing I don’t understand is your comment about the low fuel sensor. The sender and gauge is 0-90ohm but you said the original board was reading 570ohm? I don’t understand that. I am the first to admit this electronics thing is a mystery to me, but is it possible there is a resister in the feed line to that component on the board?

[WayneG]

Originally Posted by Keyair

I think that is way cheap for what it is and I bet you will sell all 12 in a snap.
One thing I don’t understand is your comment about the low fuel sensor. The sender and gauge is 0-90ohm but you said the original board was reading 570ohm? I don’t understand that. I am the first to admit this electronics thing is a mystery to me, but is it possible there is a resister in the feed line to that component on the board?

I forgot the decimal point on the knob, it should be 57.0 ohms

[Magnet18]

Looking awesome Wayne!!
When you do your own boards, do you do any sort of soldermask application?

I tried etching my own one time, it turned into a big mess, i usually just send boards to a fab house, my projects are usually so small they're really cheap.

Anyway, i have an almost untouched bottle of ferric chloride that's yours if yours if want it, not sure how big, I think a liter

Edit
If you need any help with the soldering labor, I'm more than happy to help. All that soldering would only take me an hour or 2, and I've got flux just sitting around...

[WayneG]

Originally Posted by Magnet18

Looking awesome Wayne!!
When you do your own boards, do you do any sort of soldermask application?

I tried etching my own one time, it turned into a big mess, i usually just send boards to a fab house, my projects are usually so small they're really cheap.

Anyway, i have an almost untouched bottle of ferric chloride that's yours if yours if want it, not sure how big, I think a liter

Edit
If you need any help with the soldering labor, I'm more than happy to help. All that soldering would only take me an hour or 2, and I've got flux just sitting around...

It has been over 5 years since I made my last board but it is easy and fairly reliable.
I use a cad program to build the foil pattern as viewed from the component side, then I use a laser printer to make a photo mask for a board with a pre-sensitized coating. Expose it to a sun lamp and run it through a developer and then into the acid bath. As long as you use fresh chemicals it is usually a very sharp copper pattern.
Before the cad program I use to do the pattern on blank transparencies with black tape and rub on solder pads made for the job. That took a lot of time.
As for chemicals I already ordered them and the pc boards. I am still refining the circuit and artwork.
I will see how much work it is to populate the boards, with a low component count, I am guessing about 1/2 hour per board.

[WayneG]

As of today, all the parts are ordered to build 12 modules, if I dont need to spend any more on them, I figure I will be under $40 a module, shipping included.

A questing for all of you with module problems;
Which lights do you get false triggers on most?
I ask because all 4 circuits use slightly different methods.
For me, in my MH;
I get water in fuel light coming on most often, that is with no sensor connected.
I also get low coolant occasionally.
My low fuel readout always worked, but I dont recall if the low washer light ever came on?

When the parts come in I will verify the PCB artwork matches the components and then start making boards.

[Keyair]

That's an amazing price Wayne!

Obviously, you have my unit on your dissection table, but my water in fuel light was always on... the low coolant and washer fluid was on sometimes, even tho I had bridged the sensor cables. Some of my lights came on when I put the headlights on and some blinked with the blinkers....
I suspect some of that was voltage drop and/or ground issues...

[Waipio Rim]

I have not kept close track but it sounds like our '90 345 acts pretty much like yours with the water in fuel and coolant lights keeping me continuously entertained while I drive. I only get the occasional coolant light on our 310 and I suspect that is a sensor problem as it came up after I changed the overflow tank. I don't recall ever seeing a low fuel light. Anyhow, if you have any leftovers please put me down for two instead of one.

[WayneG]

I dont think the fuel level circuit will give us a problem, but the trip level for low fuel was high on the module I dissected (Light on at 1/2 tank) I added a adjustment so that can be changed.
The washer level is a very simple circuit and I wondered if it gave anyone a problem. I am making provisions on the circuit board if it does need adjustment.
The water in fuel and coolant are the oscillator based circuits and I did need to trim the sensitivity in the coolant circuit but not in the water in fuel circuit. I will also leave room in the circuit for a trim pot for both.