Since I am a mechanical engineer, a lot of the thinking required for programming these AVRs hurts my head. Not literally, but I find I spend a lot of time wrestling with thinking through algorithms and getting confused and having to start over with the thinking process. Also, it takes me some time deciphering the syntax of C. I definitely feel like a fish out of water. :shock: My method of dealing with this is to take breaks and do things that are less intellectually strenuous.
I have made a lot of progress on the tachometer code but I have taken a few breaks along the way. Here is what I am doing for some of those "breaks"....
My first post with the AVR Freaks listed projects I want to make. The first item on the list was the tachometer I made in this thread.
The second item on the list is this Manifold Pressure (MP) gauge. Here is an image I showed in that first post...
When I made the bezel for the tachometer, I made an extra, since I knew I would be making this gauge. However I needed to make a different diffuser for the LEDs since the display is slightly different. Here are some images of the process...
I start with a piece of 1/2" (12mm) white translucent acrylic and machine away a pocket, leaving trapezoidal 'islands' that will be light pipes for the LEDs. The large rectangular island below is for the seven segment display area.
Since the LEDs are pretty close together and there wouldn't be enough space between the trapezoids for the cutter, I only cut every other one. I then make a separate part that fits on top and extends the remaining trapezoids between. The rectangular island is where the nomenclature "MP" is below the digits.
This is the middle, top, and bottom segments of the seven segment digits being cut.
The two parts of the diffuser "mold". After the vertical segments are added, the two parts will be cut out of the larger piece of acrylic.
This is the vertical segments being cut - note the pins left on top of each one.
The vertical segments are broken out. The pins fit into holes drilled in the bottom of the pocket with the vertical segments.
All segments have been added including a decimal point. Epoxy has been cast around them, along with pieces of aluminized mylar (from a fiber bar wrapper) to make an opaque barrier between segments (to minimize light 'bleeding' between segments).
You can see the perimeter of each part has been cut. There is still a thin section of plastic left that will be easily broken to release each part.
Slots are cut in the top plate to allow epoxy to be poured into mold.
The mold is assembled. Pins in the corners locate the top to the bottom and screws hold them together. You can see pieces of aluminized mylar inserted between each trapezoid. The holes around the perimeter allow bubbles to escape when epoxy is added.
A close-up of the aluminized mylar strips between each segment. You can see how close together they are.
Epoxy has been added. It bubbled up quite a bit when put in a vacuum. The diffuser for the tachometer didn't get the vacuum treatment and had several large bubbles in the finished product.
The bottom (back) of the 'mold' is machined to expose the epoxy and segments. Here you see slots being cut for the LEDs to protrude into.
The top (front) of the 'mold' is machined down to the proper thickness of the diffuser. The perimeter is then cut down to leave a thin section of plastic.
The finished diffuser is broken off the remaining parts of the 'mold'.
Since the two circuits are very similar, one of the PC boards of the tachometer is used in the MP gauge. The difference being, one of the PCA9922s is left off along with eight LEDs. Also, three jumper wires are added (fortunately there are vias in the PCB that allow these wires to be easily soldered in place).
The PC board was originally intended to allow some HP seven segment LED displays to protrude through a rectangular hole in the middle. Here you see a small PCB was added in this rectangular hole. Since this PCB was designed for the tachometer with four digits, the hole is larger than required for the three digits of the Manifold Pressure gauge. However, after beginning the construction of the diffuser, I realized that there was no provision for a 'units' display. You can see on the finished diffuser that there is a rectangular area of acrylic to the right of the digits.
Another small PCB (a section cut out from another unrelated PCB) is part of what fills the rectangular hole in the middle. This small PCB has a place to solder additional LEDs to back light "In Hg" as the units on the right of the digits. In the image below, you can see that the last eight 'slots' for LEDs on the arc are not populated. The seven segment LEDs have not been installed yet.
The diffuser, engraved face, and tinted lens have been assembled. You can barely see the "In Hg" nomenclature to the right of the digits.
The above PC board is the display board. Next I will populate the CPU board and then connect the two. After that, it will be back to software.... :shock:
Cris
