Today my Linear Tech LT3080 LDO voltage regulator arrived in the mail. Will post an update once I get it breadboarded. Some fun ahead!
Monthly Archives: November 2013
Tonight I took advantage of the milder temperatures and soldered a few SMT resistors onto a scrap PCB as practice. It went smoothly, with the exception of Q1, which hopped when I applied too much pressure while tacking it down. While it looks a bit goopy, it tests out alright. Still a bit too much solder on some of the Rs. Unfortunately I do not have any magnification other than my camera lens, so it’s hard to inspect my solder work in any great detail. Clicking on the photo above does offer a bit of zoom, however. Particularly pleased with R1. A definite improvement over my first attempts. Looking forward to more practice with finer pitch IC packages.
Power Supply Update
After watching Dave Jones’ 5-part lab power supply series, I’m beginning to grasp some analog circuit basics and am eager to try breadboarding my own constant current/voltage supply circuit. To help me design my own power supply unit, I’ve ordered IC samples, capacitors suitable for decoupling/noise reduction on the supply line and op amp bridges, and resistors with a suitable tolerance for the voltage shunt/current sense amp. I was able to scavenge two sturdy potentiometers from some old electronics to feed the op amps in setting the voltage and current levels. Other components, such as the 12-bit DAC, will allow a micro signal the op amps and adjust the current and voltage at a decent resolution (0 to 4096). Jones’ schematic shows two single-turn potentiometers accomplishing the same task.
Part one of a series produced by Dave Jones of EEV Blog where he covers the steps in designing a regulated variable lab power supply based on the LT3080 voltage regulator and LM334 current supply. This design is of interest as it is a simple design that allows for control by MCU. After looking at the commercially available units, I’ve decided that designing and building my own is the best route. This will allow me to include custom features like a display showing total current drawn by the load with min/max reading, as well as switches to turn the supply lead off without shutting down the entire power supply.
Rewind to September and I was finishing my first solo project with the Teensy. After completing the tutorials, this was my first project in Arduino C++. It’s made up of two rows of 3 white LEDs that cycle on and off to create a marquee effect. A push button swaps the direction and a potentiometer adjusts the speed of the loop.
It’s alive! No explosions or burns. *phew*
With my new SparkFun variable temperature regulated solder station from Spikenzielabs.com, I’ve been able to practice more SMT work without crummy tools hampering my efforts. Following the tips from EEVblog, I’ve had some good success with the tack and reflow method. My square pad / through-hole combo proto boards offer a bit of a challenge in that the solder tries to escape through the holes when preparing the pad for an SMT component. A small bit of masking tape covering the other side stops this nicely.
Examining the “scrap” (there’s no visible damage) Solder: Time II board from Spikenzie, I was able to determine that it’s an older revision. Since the current schematic varies but the components are the same, I was easily able to determine the values of the resistors and capacitors. The main different in this older version is that each button uses its own pin on the ATMEGA328P, whereas the current revision sees the 2 buttons share one pin with a voltage divider. All easy enough to decipher with my VOM‘s continuity test.
Everything tested out great on the first go. Neglected to solder down the other side of R4, but this will be a quick fix tomorrow. Will attempt to solder the ATMEGA TQFP at that point too.
I also changed the charge current limiting resistor on my TP4056 linear charger. The stock 0603 1.2K ohm resistor was replaced by a 5.1K 0805. “But Mr. King,” you might ask, “isn’t this a mismatch? 0603 and 0805?” Yes, I would reply. It is a mismatch, but it turns out that the pads are big enough to accommodate the slightly larger package. After removing the 0603, I sopped up the stock pasty solder and then applied flux. With just a small bit of solder onto the first pad, I placed the 0805, and tacked it down. Then a tiny bit of solder on the other pad. Straightforward!