Evan at his Techie-Blog writes,
“While writing the article on multiplexing the esp’s inputs I came up with the idea of PWMing all the outputs at once by interrupting the path to ground with an n-FET. That’s actually not a bad idea, and I have an extra input on the analog MUX that I can use for a light sensor so I can even have auto-dimming. This is to describe how I did that.”
With much difficulty and frustration. That’s how I did it. If you hadn’t figured it out yet I wrote the intro to this piece before actually preforming the task. The main problem is that for some reason I couldn’t get input 0 of the analog mux to do anything. As I think about describing my problem here I also may have the solution… f**k. The problem is that any input to that input was pulled very very low to the point of pulling more than an amp at a half a volt. I swapped the chip but it continued to happen. What I didn’t do was check for a little solder bridge (would have to be very little) to ground which could be what caused the pull down and uselessness of that input. In order to get around this I added another control line for the mux to use the other inputs. An act I now realize could have been to move s0 to s2 and tie s0 high so I had to use the other bank of inputs…I was having a good night until I go to write it down, I swear.
So, with a cadmium sulfide cell acting as half a resistor divider I can read the local light level. That information could be used to dim the LEDs if I had that ability. It turns out that when I wired the LEDs I tied them all to the same ground wire, one not shared by any other things. I decided to break the ground wire just before it hit the ground plane and stuck a 2n7000 FET with pull down resistor on it. This is called “low side drive“, a technique I have paired with individual”high side drive” pins coming from the ‘595. Since the shift register can only update all of the LEDs at once I decided that PWM through SPI is more convoluted than I want to write code for. The reason I want dimming is so if I mount this on a wall in a room of my house I can have the LEDs not be obtrusive while still being visible. That means all I need is to dim them at once so I spend an extra output to control the brightness of all the LEDs at once.
That sums up all the hardware changes I made, if you take a look at the code you will find that I have put in a lot more commands, I have moved some things out to functions, and that I have defined masks for reading/writing bits rather than having hard-coded sequences. I rather like my new code, but one thing I’m going to move toward is having many topics on each device. The problem with defining the topics now is that if I don’t know where I’m going to put things or how I want them to interact then I can’t design a system. The problem I face as being not-a-programmer is that I don’t know a good way to parse the payload of a message. What I have right now is to have a lot of verbatim answers or an’else’ which I use for numbers. First: I should move to a switch/case structure, and second I could stand to parse a smaller part of the payload making my code more versatile. I’m not going to do the second one,I will instead move to a lot of topics which contain ‘/’ symbols so it looks like a hierarchy even though it isn’t.
here is the bit of code I updated.
here are the pictures (again).
here is my hub for all things esp8266.
More info at Evan’s Techie blog.