Lambda display for digital wideband controllers

[baldur]

I decided I needed a display to go with my PLX SM-AFR wideband controller and I didn't really like the PLX displays, the digits are too small.
So I dug into my parts drawers and built a display from parts I had around, a very expensive Atmega32 I bought years ago but never used, some 7 segments I got off ebay years ago and other small bits. First time I ever use an AVR for a project, I've used most other microcontrollers.
The code is for getting data from a PLX display, but it could easily be adapted to get data from any other lambda controller that transmits RS232 data (such as Innovate)

Mostly finished board. Has crystal there but I ended up using INTRC at 8MHz to save space.


Routed with a bunch of kynar wire on the back of the veroboard, all passives are surface mount. I left space for extra LEDs below the display.


Plastic work is not one of my strong areas but I think it came out ok. Case is only 15mm thick.


Schematic I drew afterwards. Does not show the ISP header or the crystal, both were removed before stuffing the board into that small box.


Firmware source code is attached, it's in C written for avrgcc using avr-libc. Based on some example code from the avr-libc distribution.

[Fred]

Cool :-)

Offline I asked if it will build easily on lesser chips and the answer is yes. Making it read AFR is of course even easier. It's just the protocol to sort out at that point. Does anyone want to post the protocol innovate use? Perhaps someone could hack it up?

Thanks Baldur, most appreciated!

Fred.

[baldur]

Innovate will give you the protocol if you just ask, I have it here but I don't have their explicit permission to share the document. The PLX protocol can be found on the PLX web site, called the iMFD serial protocol.

[toalan]

I just got my board back today from batchpcb for a universal display. It runs off the 0-5 analog output, it should work with any controller that has a linear output. It is not as nice as having a numeric display, I will do an alpha numeric one that runs off 0-5v next. I am gong to release the gerber files and the source code for the displays. The display uses an attiny261.

Here is a video of the current display
http://ca.youtube.com/watch?v=gEelEZB6o4U

The thing clamped to my table is my wideband controller, it also has a display. The thing hanging from the 3 yellow wires is the display.

Regards

Alan To

[baldur]

I went and made a second display yesterday, this time using a surface mount Atmega8535 I had around. It can run the same code with only modification being to edit the makefile to reflect the change in processor.
The idea behind this display is to capture speedometer signal and injector signal to display fuel consumption rate both per distance and per hour.

Printed a single layer 100x160 euroboard, managed to panelize 4 boards in that space. This time I managed to make space for a crystal and the ISP header on the board.


All passives + MCU are surface mount. Had to fit some jumpers as there's only one signal layer.


ULN2004A is a 7 channel logic input darlington array, had a drawer full of them donated by a colleague. This reduces the thermal load on the processor which is nice with a chip in a smaller package. The corners of the board are rounded to fit around screw posts in the cases I'm using.


0402 caps, quite handy but I wouldn't solder them without the microscope.

[toalan]

Nice work.

I was just going to say that driving the LEDs directly using the MCU causes alot of noise, it is not a real problem if you are not using the ADC. The darlington driver IC is a good addition. Alternatively you might want to try using a dedicated 7 segment driver IC such as the mc14489, it is quite costly ~$3.25 in qty of 100. They make the display really bright and flicker free. Also you can connect several mc14489 ICs in series with the SPI bus to create a ghetto digital dash.

Take a look at the atmega48/88/168, they seem to offer the most peripherials and features for an AVR under $5.

If you are interested in working with me, I would like to create an app note for a wideband that I am going to release in spring. It would be a kickass app note if the display could also work with other wideband controllers. Would be awesome if the display could show info about fuel consumption as well. firmware and gerber files will be released to the public.

Currently the plans are for the display are:
-supports a 4 digit LED display
-uses a mc14489 LED driver
-Support for all widebands using the 0-5v input
-Special support for my wideband using I2C
-uses the atmega48/88

I have driven a mc14489 using a atmega88 in another product I worked on, so I already have much of the work completed. The parts I am missing is RS232 protocol for innovate/PLX/etc.. and the MPG stuff.

Regards,

Alan To

[baldur]

Yeah, I'm not using the ADC on this board, if I was I would've done more about power supply filtering too, it's bound to be pretty noisy with a couple hundred milliamps being switched from that 7805, too noisy for decent ADC performance at least.
Obviously, latched outputs are ideal so the display gets it's full brightness and doesn't need to be constantly updated.
If that driver is so costly another option is to use addressible latches for the digits, but that would come at the cost of board real estate, which in this design is kept as little as possible. More tricks could be done on a proper 2 (or more) layer board though. The easiest way to stuff more into a case of almost the same size (slightly thicker) would be to place the processor and signal filtering on a seperate board that stacked underneath the display board.

[toalan]

I just finished the firmware and the pcb for my open source AFR display.
I have broken the project into 2 parts; Driver and Display. The Driver is an Attiny861 with the required voltage regulator and protection, the display is the; 7segment Display, current limiting resistors, and 4 BJTs. Breaking the project into 2 boards makes the display pcb the same width and length as the 7 segment display so that you can fit it almost anywhere. Also I can resuse the Display board in other designs. A ribbon cable will connect the driver to the display.

It reads the AFR from an analog linear voltage output, so you can use it with any wideband controller.

I just submitted the PCBs to batchpcb, so I should get them back in about 2 weeks. They should be very nice looking and small units, I will post pics once I get them.

[Fred]

Cool! :-) Thanks for sharing!

[jharvey]

Looks like you're using Eagle. Is that right? I'm also curious if you have posted your firmware some where?

The pictures look good. Keep it up.