I have mentioned this in previous posts but I am one of those people that goes a bit crazy with holiday lights. I do the whole computer controlled setup utilizing LED lights that are individually addressable. (This post got a little long, if you would like to skip some reading jump down to “the challenge” part)
The why
The controllers to run these lights vary in price and I have a number of them as I have added more lights. I recently moved to a new house that has a much bigger yard (I didn’t have a yard before). Bigger space means both that I will spread the lights out more and possibly add more over time. I have two varieties of lights, some run on 12 volts and some run on 5 volts, the control signals are the same. The controllers I have used thus far connect to the computer by wired Ethernet and then connect to the lights. There is a limited distance that the signals from the controller to the lights can run before they begin to fail. I have some controllers that can run around 2,000 lights and some that can run around 10,000 lights. So far I have been placing the controllers as central as possible and keeping the runs as short as possible, this will be difficult with the new space. 10 to 15 feet works fine after that it gets dicey, It is possible to extend the distance but not easy.
The solution
A few years ago a diy wireless type of controller entered the market. This controller is based on the ESP8266 module and uses the inexpensive esp-01 version. This method is mostly due to the programming skills of one person. This module runs on 3.3 volts although the lights require a 5 volt data signal so it is necessary to shift the logic levels. Because of this shift, it requires power with both voltages. Since the lights run on either 12 or 5 volts so your power supply will be one or the other. The solution for a while was simply to have a 5v and 3.3v regulator and a jumper to switch out the 5v one. Last year the creator of the controller introduced a board with a buck boost converter that doesn’t require jumpers.
The problem
The boards being sold that work at either voltage without jumpers are $20 and since I need about 50 boards to control all my lights and I like to solder I am seeking a less expensive diy approach. That board utilized a TPS62175 buck boost converter although that is capable of passing the 5 volts through. Most step down and step up converters will not work when the input and output voltage are the same. The TPS62175 chip is a surface mount chip that requires an oven for soldering, also it costs about $1.50 when purchased in small quantities. The coils and capacitors necessary to make it run add more cost. I wanted a more diy approach ideally something that is through hole and with minimum cost but would do the same thing.
The challenge
Keeping costs as low as possible make a power supply that will work from a 5 volt or 12 volt input and output both 5v and 3.3v no matter what the input is. My first approach was to purchase various step down converter modules to see if any would work taking in 5 volts and putting out 5 volts, none of the ones in an affordable price range did. I did have a thought about utilizing the 5v regulator setup and creating a comparator circuit to automatically short it out when the input is 5v, although I didn’t explore that option.
The approach
My first approach was to use a cheap step down converter to go from 5 or 12 volts down to 3.3v and that seemed to work fine. I then used a step up converter to go from 3.3v to 5v and that worked. I connected the esp-01 module and logic level shifter and it did indeed control the lights just fine. The one issue I discovered with this setup is that depending on the wiring when the lights drew the max current it was possible for the voltage to dip. If this dip went down to about 4.75 volts the 3.3v step down stopped working. My second approach reversed the setup so I stepped up the input to 15v (just needs to be something above 12) and then I stepped that down to 5v and used a 3.3v regulator. This setup also worked and proved much more voltage tolerant.
The cost
I used a step down converter commonly referred to as a mini360 and a step up converter called an MT3608. In quantities of 10 the step down was about 32cents each and the step up was about 41cents. The ams1117 3.3v regulator was about 3cents, for a total cost of 76 cents for the power conversion circuit. I suspect the power quality isn’t great (I didn’t put it on a scope) but it worked fine without any filtering caps although I may add some.
The question
I don’t love the idea of chaining a step up and step down converter to do what one part can do, it just isn’t an elegant solution. What do you think is this a bad design? Do you have a better solution that would be at, or lower in cost but achieve the same results?
For reference
These are links to some designs I discussed and you can find schematics on the pages.
http://forkineye.com/wp-content/uploads/2016/09/ESPixelStick-V2-Assembly-and-Usage.pdf
https://www.doityourselfchristmas.com/wiki/index.php?title=ESPixel_Stick_%26_ESPixel_Pops
Step Up and Step Down
Re: Step Up and Step Down
