Wednesday, December 26, 2012

Learning to Solder and Soviet Logic Chips

After soldering on the LEDs of my RPN binary calculator, I went on to solder the resistors and the 595 shift-register. Unfortunately, this didn't go as well as soldering the LEDs did! I had a lot of trouble getting the solder to flow and the 595 chip ended up getting really hot and may have been damaged. I definitely used too much solder too. Eventually I had to stop soldering because the tip of my soldering iron wore down. I was using steel wool to clean it between joints and this took out chunks of the tip until there wasn't enough left to properly heat the solder any more. It looks like I will need some practice before I continue!

From what I have heard, a good soldering iron tip should have a copper core and be coated with other metals. The cheap tip I was using seems to be made of only one kind of metal. The only other tip I have been able to find is solid copper. We will see how long I can make it last. One good thing about it is that it is wedge-shaped. Many of the soldering iron tutorials I have read recommend a tip like this but most pictures and videos show people using conical tips. My plan is to see how well this tip works and do some practice before I continue working on my calculator.

In order to practice I got my hands on some Soviet era logic chips. They were available locally for a cheap price and I don't need to worry about destroying them if I get them too hot. Before sacrificing them for the greater good, I decided to hook them up on my breadboard. The two I tried were K155LA8s (К155ЛА8 in Russian). According to Chip Directory, LA8 is equivalent to a 7401 chip, which has four NAND gates with two inputs each and open collector outputs. This means that the chip should sink current instead of sourcing it when an output is true. Using an LED to test with, I couldn't get the chip to sink any current but when I hooked it up the other way around, it sourced a small amount. This makes me think that the chip is actually equivalent to a 7400. Also, despite what I read on this website:, pin 14 is ground and pin 7 is Vcc, not the other way around. Interesting indeed! The LED I used to test with glowed very dimly, which is to be expected since TTL chips can't source very much current. To remedy this, I hooked the chip up to a transistor labeled "HHE 8051S." (I don't remember exactly what this was salvaged from.) To my surprise, the LED glowed much dimmer when it was driven by the transistor because I had it between the transmitter emitter and ground. Hooked up between the collector and voltage it worked just fine.

Monday, December 3, 2012

Makeshift Soldering Iron

It turns out that temperature adjustable soldering irons are a little difficult to find here. In place of that I tried using a cheap one I found for a little over a dollar. It quickly got too hot and the tip turned black. Solder on the tip beaded up and I couldn't get it to tin correctly. Later I found another soldering iron that was more expensive but I had the same problem. So, I invested in a dimmer switch for lighting and connected my soldering iron to that. After about five minutes smoke came out of the soldering iron and it stopped working. After replacing it I was able to tin it correctly. One thing I noticed is that the iron never gets as hot using the switch as it did without, even when the switch is turned up as high as possible. So far I have done some soldering on my RPN Binary Calculator and it has worked fine. Hopefully this will continue working until I can find a better one. Here is a picture.

Sunday, December 2, 2012

First Project

After flashing a few LEDs and reading a few buttons with my new MSP430 I decided to start work on a simple calculator. For output I am using eight LEDs to show the numbers in binary. To do this I am using a 595 shift register. Since I am using an MSP430G2533 I would have enough pins to light the LEDs without it but I wanted to practice using shift registers and be sure I would have enough current. For input I am using a 165 shift register. This will give me room for eight buttons. I have always been a fan of Hewlett-Packard's line of RPN calculators so I decided to use this notation for my calculator too. The eight functions I decided on are 1, 0, dupe, swap, push, pop, +, and -. Programming these simple functions was not difficult. After I saw that everything worked fine on a breadboard running from a coin cell battery, I started soldering it onto a piece of protoboard. This will be good practice since I have never soldered anything before. So far only the LEDs have been soldered but I hope to finish the rest soon. Here you can see the protoboard and the breadboard with the parts of the circuit that haven't been canabalized yet.

Saturday, December 1, 2012

555 Timer Setup

Recently I set up a 555 timer and three AAA batteries to experiment with. The first thing I wanted to do was flash an LED. I wrote a program that will let me figure out the frequency of the flash, size of the capacitor, or the values of the resistors. I decided on a 10uF capacitor and a 100k resistor to give me a blink slow enough to see. This was interesting but then I decided to put a potientiometer in place of R2 so that I could control the rate of the blink. I also put a potentiometer in place of the resistor to the LED so that I could control the brightness. Tuning the potentiometer so that the LED wasn't very dim or very bright was difficult. After doing some reading I saw that it is possible to adjust the on and off times independently of each other if you use a diode with R2. I replaced R1 with a potentiometer so I could control both the length of the flash and the pause between flashes.

Next I connected a piezo speaker to the timer. It ticks every time the current to it is switched on or off. According to the datasheet, the current doesn't have to be turned off but should actually be reversed. I am not sure how to do this with less than four transistors. By using the potentiometers to make the timer pulse quickly, the ticks of the speaker come fast enough to blend into a tone. I tried using smaller capacitors from the TV I took apart with the timer and the tone was much higher. I put another potentiometer in place of the resistor to the speaker to control the volume. One thing I noticed is that the speaker made a growling sound when I tried to turn the volume up too high. It seems that the timer was failing and restarting many times a second because the circuit was drawing more than the 200mA the timer can source. To remedy this I put a resistor in series with the volume potentiometer. This is also a good idea for the other potentiometers so that the timer and LED don't get damaged either.