nofalls

Tom,
the price could go down if you used https://www.sparkfun.com/products/11113. FTDI cable would be required to load the sketch but if the pot can do all the adjustment the end used would not need one.

Tom M'Guinn

Great point -- that could cut the cost in half probably. I used the nano because it made testing software so easy, but you're exactly right. I'm pulling together a little page with the schematic and code I used so folks can improve/modify as they prefer. Would be nice to put up a pcb file too but would need someone to host that. If you're an eagle guy and want to do a board file for all just let me know.

nofalls

Tom - I am happy to help in any way I can. I can write up a BOM with Digikey PNs too.

Have you ever seen these guys? I had a board made there. 10 50mm x 50mm, two sided and plated through hole for about $10. http://www.seeedstudio.com/depot/fus...html?cPath=185

-Mark

gregeast

Keep up the good work guys, I love getting to "hang out" with the cool geeks

Tom M'Guinn

I took a stab at a web page showing the basics on how I did this. There is a link to it on the front page of my site listed below. Would like to get a downloadable PCB going, but am not much of an Eagle guy.... (hint, hint....).

nofalls

Tom - Nice write up! I put together the Eagle files, gerbers and digikey parts list. Once all of that is done I'll send it to you for review/comment/red lines. If you do not mind I would like to try to layout the board to be 2"x2" at most. That will keep the board cost down.

Mark

Tom M'Guinn

That would be great. The board can indeed be much smaller. I was using the fixed board size they give you on the expresspcb 3-1 deal, but subsequently was able to squeeze two boards on each, so can cut them in half and have two boards that are 1.25 x 1.9". That actually brings the cost down to under $10 a piece, but you have to make at least 6. Gerber files would be great -- if you wanted to design one and posted it on batchpcb for others to buy, I'd be happy to link to your product on my page. Batchpcb has a marketplace where you can post your design for others to buy, and even make a buck or two if you want. That would be a great way for the non-electronics types -- so they just have to stuff the board and be done with it.

Techno Duck

Tom, now you need to make one to fix the fuel level gauge .

gregeast

Yeah Tom, quit yer slackin' off!

DucK: There was some discussion on this on the gauge cluster bench testing thread

Laust Pedersen

Tom, can these gauge correction circuits correct for non-linear errors?

I am sure there is a need/market for a small and easily programmable box for gauge corrections with both analog and digital inputs (tachometer).
My Jalpa, for example, has a tachometer showing too high value at idle (about 20%) and too low value near redline (about 10%).

Laust

Tom M'Guinn

Laust, the basic approach in this project would work equally well for a tach (at least those like the 951 what are triggered by ignition ground pulses). As for linear v non-linear, the short answer is yes. The correction factor is done in the software, which can be written however needed. The Arduino measures the incoming pulses and then can create any output it wants. My speedometer was consistently 10% fast, so I just changed the pulse by 10% across the board. However, no reason at all the correction correction could not be more complicated. If you can reduce it to a single mathematical function across the range, you could have an elegant firmware solution. Regardless though, the Arduino is plenty fast enough for conditional correction factors such as:

if signal=idle speed, then make it 20% slower
if signal>idle & less < 1k, then make it 15% slower
...
if signal>5k, then speed it up 10%

That said, it sounds like your Jalpa tach is off in a linear way, sort of, such that something like this concept might do it:

RPM_FACTOR = ((CURRENT_RPM)/REDLINE_RPM)*30%
TACH_CORRECTION = 20% - RPM_FACTOR
MODIFIED_TACH = ORIGINAL_TACH - TACH_CORRECTION

Tom M'Guinn

Tough crowd... I'll start a new thread on the fuel gauge and see what I can do. Its problems seem to be different in nature than the speedo and tach, but easy enough to solve with some effort...

gregeast

nofalls

Tom,
this is the foot print I have for the Nano. Funny thing is the A0-A7 pins appear to be backwards from your schematic. Which is right?

Tom M'Guinn

Hmmm.... here is a picture from the Arduino.cc site, which matches the Nano's I have...