An update on some of the odds and ends of small projects and things I have tinkered with recently.

Halloween Pumpkin


For Halloween I took an old pumpkin decoration and placed the WS2812 RGB LED strip I got from Cisco at Acrobotic in the bottom. I taped an Arduino Trinket Pro board on the back and just ran the example rainbow cycle code. It of course stayed outside, and sometimes inside, around Halloween. I used a 6 volt lantern battery to power the whole thing. I initially tried running the LED strip off the 5V regulated output of the Trinket Pro board but the current draw caused the Arduino to stall. Instead I powered the LED strip from the battery directly since due to voltage loss I measured was almost exactly 5 volts at the point the power goes into the strip.

Old Phone Battery Substitute


I have an old Android phone that has a decent camera on it. I no longer have working batteries for it, nor do I want to buy any, so I decided to power it directly from DC. Just putting power to the USB charger port without a battery doesn't let the phone power up. So I decided to try and power it by giving it DC on the battery terminals. Just hooking up the positive and negative terminals also does not work. Of the four terminals one of them is for a thermistor. The phone will not power up without some resistance through ground on this terminal. So I found a resistor, I forget what value, that allows the phone to boot up without shutting down later because it thinks it is over heating. However, the value I chose is not idea as the phone thinks the battery temperature is something nonsensical like -47 degrees Celsius. I used a DC-DC buck converter and, naively, initially dialed it to 3.7V, since that is what the battery says on the outside. Apparently this is the empty voltage of these batteries and the phone would only power on briefly, blink a red LED and then turn off. Ramping up the voltage to something like 4.2V allowed the phone to come on and display the battery level as nearly full. However, I did notice some issues with the phone's touch screen being slightly unresponsive. However, I remember the phone acting this way occasionally whenever I was charging it.

ATX Power Supply


I had an existing ATX power supply converted to a "bench power supply", but it had a very noisy fan. I recently bought the Dangerous Prototypes ATX breakout board to build myself a new one. I pulled the power supply out of a 10+ year old Dell desktop. I was pleased with how much quieter it is. I cut off the unneeded wires but left enough length that they could possibly be used in the future. I taped them together by color so there was no possibility they would short against the case. I then marked and drilled holes for brass standoffs to mount the board on the top of the case. I tried to thread the holes with a screw but despite this the metal was not thick enough and the brass too malleable that they stripped easily. To secure them I used JB Weld on the threads. But, I must admit, one of the standoffs is just slightly off and I did not do a perfect job of drilling the holes. I think this is an excuse for me to buy a small drill press.

DDS Signal Generator


I recently purchased a DDS signal generator board off eBay that uses the Analog Devices 9850 chip. I haven't done anything with it beyond putting it on a breadboard and hooking it up to an Arduino Pro Mini. I used these instructions and sample code. Only 4 wires are needed to program the frequency when using the serial programming mode of the chip. I confirmed it works by watching the signal output on my oscilloscope. What I eventually want to do is try and use the board to replace the crystal in an old FM radio transceiver.

Looking at the date code of the 9850 on the board I saw that it reads '04. The chip is a decade old already, which explains how these boards can be so cheap on eBay when the chips themselves are an order more expensive. I have a 9851 in my parts drawer that someone gave me years ago and even it is newer with a date code of '06.