Friday, October 15, 2010

Adjustable power supply with LM317

LM317 is a cheap chip with 3 pins. It is widely known as one of the most basic microchip for adjustable power supplies. It is capable of working with 30 V and 1A current. However, it has quite a big voltage drop, around 1.5 Volts. Here is the pin out of the microchip:

LM317 comes in several packages, but TO-220 is the most convenient one, because you can easily get snap-on heat sinks for it.

The LM317 is not very good for "laboratory power supply" but for tests and troubleshooting it can go preety far.

This is the circuit that i have used to build one myself (note that this circuit is taken from original data sheet, but there is a mistake, pins 2 and 3 are swapped there. This is the right version!)
As you can see, there are only few components used.
1. LM317 microchip
2. 1uF electrolytic capacitor (The black stripe in circuit is anode (Negative; -))
3. 10uF electrolytic capacitor (The black stripe in circuit is anode (Negative; -))
4. 0.1uf ceramic capacitor
5. 240 (200 or 270 is also OK) ohm 0.125W resistor
6. 5K mono linear potentiometer
Optional parts:
7. Any LED.
8. 1k ohm 0.125W resistor

The pricing of all these things should be around 2$, or if you have resistors, capacitors and LED lying around it will be around 1$.
Sorry, but i wont be able to show you any photos if me making it - my camera is at the other town (im studying) at the moment, but heres a picture to see how small it actually is:
It is cheap, small, does not heat at all, but its hell useful! Try building one yourself!

Friday, October 8, 2010


For some time already, people are experiencing the problem of incorrect grounding. Most young (and even advanced) hobbyists/engineers think the the "negative wire doesn't do anything, i will just connect it to ground". That doesn't do anything bad in circuits which do not involve video or sound. However it makes a huge interference and additional noise in sound and video applications.

When you are grounding, you want to connect all grounds to one conductor, which should have same potential, however if you connect some ground outputs to one conductor at different places, the conductor will have small, but different potentials on its body. This is called a ground loop. To avoid this you can keep on these instructions:

1. Star ground principle. This photo (not mine) illustrates that pretty clear. Every ground should have its own wire, and they should be connected to the final ground wire at one point.
2. Ground wires should be as short and thick as possible. It would be best to use monolithic wires for this purpose.
3. If you are making an amp with two modules, make sure it is symmetrical and the ground wires are exactly the same length.
4. If you are shielding inner wires, the shielding should be connected only in ONE side. If connected to both, it won't be a shield anymore - it will be a bad conductor, which will generate trash sounds even more than if it wasn't shielded at all.
5. Divide signal and power grounds. In that way trash sounds from power line will have harder way getting to your speakers :)
6. Ground wires shouldn't cross other ground wires, or AC ones, which would be even worse. 

The rest part applies for PCB's:
7. When making ground tracks, try to have it as straight as possible, don't do any spirals (they will work as capacitors) .
8. Ground tracks should be as far as possible from input tracks. 
9. If possible split the PCB to few parts like preamp, back amp, power supply, etc.

Saturday, October 2, 2010

How to solder

Stupid. My first post should have been this one. Well, its better later than never, so here it goes.

1. Wash your hands. It's really important, as your hands must be fat-free, or your components might get some of fat on them and the solder wont stick to them.
2. Clean your table. Make sure there's nothing that can make a static discharge.
3. Put a sheet of paper on the table. It really helps, as you can see small parts easier, and lighter background is better.
4. Lights up! Make sure that the area where you are soldering is light enough, or else it will be hard on your eyes.
5. Goggles, or at least eyeglass. Small quantities of flux sometimes jumps off your soldering iron, and it can hit you in the eye. On other areas it wont be dangerous, because when it reaches your face it isn't that hot, but on your eyes that can be pretty bad nonetheless.

6. NEVER TOUCH a hot soldering iron! The temperature of the tip can be more than 300 degrees Celsius, which can cause serious injuries.
7. ALWAYS put your soldering iron into it's stove. Don't leave it on table even for a second. It should be either in your arm when soldering, or in the stove at all other times. If you don't have a stove, go and buy one, its less than 2$, but can save you weeks of hospitality.
8. Make sure that hot soldering iron/stove has no contact with the cable. It can cause shock, and 240V isn't good for your health. Use of heat-resistant cable to avoid problems!

9. Preheat your soldering iron.
10. Clean the tip of the soldering iron with wet sponge, or even better with metal sponge.
11. Mount component that you want to solder into the holes, etc.
12. Work with that component until it is done, before moving to other parts. Rule of thumb: Big components are soldered first.
To solder correctly, first you must add the soldering iron to the component and the place where it will be, and heat those two items at the same time. After a few seconds, add some solder. Then, take solder back, and finally take soldering iron back.
13. Make sure that you solder it good:

14. Check solder places again. They should have a nice volcano shape, not a bubble, not a puddle. The solder should be shiny.
15. Don't be afraid of the fumes: its not lead fumes, it comes from flux. Lead evaporates in higher temperatures.

16. Clean the tip again
17. Start working on another component.
18. When you finish, clean the tip of the soldering iron, but leave a small layer of solder on it - this prevents oxidization, and the tip is preserver for longer time.

This should be it. If you have questions, there's comment field below ;)

Friday, October 1, 2010

Amp with 1554.

Since at the moment I'm on a budget, the easiest way to get some sound is gainclone amps. One of the cheapest and quickest to build would be TDA1554. Its cheap (3-4$, or 12 LT in Lithuania) and requires very few external components.

For the amp you will need:
Chip (TDA1554)
Some electrolytic capacitors - 2200uf, 47uf, 100uf, 10uf.
Ceramic capacitor - 0.1uf
Resistor - 39kohm
Potentiometer - stereo logarithmic if you want to have sound control on the amp.

Heres the tadasheet for TDA1554:

Simple schematic (taken from datasheet)

Heres the gif showing the PCB layout:


I won't be making it during weekend, but i should be able to make it Monday or Tuesday. Well, good luck to everyone!