Re: My home-built DIY gear position indicator - includes plans
Good stuff msi1259
...Automotive PTC resettable fuses (i.e. Tyco RXEF050), are easier to mount (through hole), they reset on power off (allows box to be sealed / potted), and are cheaper then glass fuses.
Agreed... I love these things... I just don't/didn't have any in my junk box inventory when I started this little project. I'm gonna have to update my junk boxe's inventory to keep some of these on hand in the future.
...Possibly instead of using a Learn button, use logic conditions on power on - in Neutral and Clutch in while key is turned on causes Learn mode code to run?
Hmmmm, great idea. I can see using this technique to signal the MC to
enter "learn" mode. It's the interactions that need to occur, once in "learn" mode, that I can't quite get my head around. How would you signal the MC to proceed from one step to the next, in the learning sequence? And how would you signal the MC to "[re]learn" the current ambient light conditions?
I'm gonna have to noodle on this for bit. I'd be interested in your additional thoughts around this.
...Use weak pullups on the port pins instead of the 10K resistors?
I did look at this once upon a time. Although the 16F88 does have em, it's an all-or-nothing thing. Either
all pull-ups are enabled. Or
none are enabled. And only on PORTB pins. Due to the PORT pin assignments, I couldn't enable
all of em. When I started this project, all I had was a 16F88 (cuz it met the needs of my initial Suzuki GPI project). Access to bunches of discrete resistors made it easy to work around. Perhaps I should have looked at another family member for the Honda GPI (call me lazy). Looking at the 16F690, it appears the pull-ups are individually settable. I may just have to get me a sample, and play around with this.
...Use the on-board comparators instead of external transistors?
This is an awesome idea. When I first started working with the PIC, I didn't understand the power & value of these little on-board gems. I was/am ignorant. I do now
...Since (most of) the PIC chips are internally limited to 25ma on port pins, and the KingBright LEDs can take 30ma, remove the resistors to the LED segments and depend on the 25 ma limit?...
Sitting here thinking about this, I'm reminded of the old story about why Mom would always cut the Christmas ham in half, and then bake one-half at a time. Turned out, it was because that's what her Mom (grams) always did. After digging a little deeper, the real reason was because grams' oven wasn't big enough to bake a whole ham at once. Mom just did what her mom did without thinking about it, even tho her modern oven was big enough
Anyhow, I digress....
I've seen this question (whether to use external current limiters or not) come up, from time to time, over on the MC forum I watch. The response always seems to be "Never Never Ever drive an LED without a current limiter". I know the PICs have a built-in protection mechanism. But, it was my understanding that this is NOT to be relied on as the
sole current limiting mechanism, else the life expectancy of the PIC may be shortened. So, I've taken the conservative route, opting to use current limiting resistors, for fear of cratering the PIC. Can the port pins
really take the abuse? Show me the docs assuring it, and I would love to eliminate the resistors
Edit: Looking at the "Electrical Characteristics" page in the data sheet for the 16F88. It says the "Maximum output current sunk by any I/O pin" is 25ma. Then at the bottom of the page, in a note, it says, in part "... Exposure to maximum rating conditions for extended periods may affect device reliability". Same statements are found in the data sheet for the 16F690.
...someone posted a video on Youtube showing this (search on pic current limt)
You mean this one; http://www.youtube.com/watch?v=TaHPKWCeYAE
...To allow use of low end programmers (such as the DV164120 PicKit 2 Starter Kit), maybe a different chip then the 16F88 (i.e the 16F690?)
I'm not sure what your getting at here. I use a PICkit 2 to program the 16F88 now (as well as others, such as the 16F886).
I do think I'll get me a couple 16F690's, and look at using that device instead of the 16F88, as I continue my endeavor to combine the GPI and speedo-corrector algorithms. Couple pins bigger footprint.... but would allow the elimination of external resistors. And using on-board comparators instead of external transistors - GREAT IDEA.
