T1W5: Finishing the LED Board
This week I would like everyone to finish soldering the LED board. We didn't have school on Monday so the Friday class will be ahead for a while.
After the LED boards get assembled we can test them using a laboratory power supply set to 5 Volts, which is what a gets supplied from a USB charger.
The Bluetooth speaker kit has four major steps:
Soldering the LED board
Attaching wires to the speakers and power jack
Assembling the components onto the case panels
Fastening the case panels together to make the enclosure
Here is a link to download the assembly instructions from the kit manufacturer.
Soldering the LED Board
We will build the LED board by inserting electronic components onto the top side of the board with the white labels, and then flipping the board over to solder the lead wires to the round metal pads on the back wiring side. We will solder the shortest components first so we can just rest the circuit board on the components while we solder.
Resistors convert electrical current into a voltage drop, and three different values come with the kit. The resistance values are indicated by color codes painted on the resistor, here is a key to figure out the values - we have 5-band resistors where the fifth band is brown and shows the tolerance is 1%.
Step 1: Solder Resistors R1 & R3
Resistors R1 & R3 have values 20Kohm and color codes RED BLACK BLACK RED (BROWN). Find the two 20Kohm resistors and remove the tape strips from the ends. Then bend the leads of the resistors down in a U shape and insert them into the circut board along the bottom edge. Spread the leads apart slightly to keep them from falling out and then flip the board over and solder the leads to the round circuit pads on the back (wiring) side of the board. When the solder joints look good clip off the leads near the circuit board and save the short bits of wire for Step 4.
Step 2: Solder Resistors R4 & R5
Find two 470 ohm resistors (color code YELLOW PURPLE BLACK BLACK BROWN) and solder them into positions R4 and R5, and clip off the leads on the back.
Step 3: Solder Resistor R2
Find the last resistor with value 2 MegaOhms (color code RED BLACK BLACK YELLOW), solder it into position at R2, and clip off the leads.
Step 4: Solder Jumper Wires J1, J2, J3
We will go out of order a bit from the instructions and solder the three jumper wires J1, J2, and J3 on the top of the circuit board. These wires just make connections in the circuit board that would have been blocked by the other wires or components. Find some short bits of wire clipped off from the resistor leads, and bend them in a U shape about as wide as the lines on the circuit board. Push the wires flat against the board and spread the leads a bit on the other side of the board to hold them in place. The flip the board over and solder the ends of the wire, and clip off any extra length.
Step 5: Solder the IC (Integrated Circuit)
The IC (integrated circuit) that controls the LEDs is the black rectangle with lots of metal leads on the sides. We need to be careful to install this part in the correct orientation, so we will only solder one out of the 16 leads to start. First, make sure all the leads of the IC are straight and lined up with each other - if any wires are sticking out, use the needle nose pliers to carefully bend them back in line with the others. You may also need to bend the ends of the leads together slightly to fit them into the holes on the circuit board - hold the leads against the tabletop and gently bend them all at once in slightly.
Find the notch on the short end of the IC and match it to the notch on the circuit board label. Carefully insert the leads of the IC into the holes in the board, and double check that the notch is on the correct side. Then flip the board over and rest it on the IC to keep it in place. Just solder one corner lead to start with - don't do all of them at once or it will be difficult to fix mistakes!
After soldering just one lead, turn the board over again and make sure the IC hasn't shifted and is flat against the circuit board on all sides. Also check again that the notch on the IC is on the side next to Q1. If needed, you can melt the solder on the one lead and reseat the IC so it's flat, or pull out the IC and fix the orientation. Ask the teacher (Tim) to check your IC before going on to solder the rest of the leads! He can quickly fix any problems if needed.
If it looks good, go ahead and solder the rest of the leads. Try to do this quickly so you don't spend a lot of time heating the IC leads (and cooking them). The leads are short so you don't need to clip the ends off.
After you have soldered all the IC leads, check your connections to make sure you don't have blobs of solder shorting between the leads on the IC. You can fix this by using the solder sucker tool to remove the extra solder - Tim can show you how and help fix problems.
Step 6: Solder the LEDs
D1 through D10 are color-changing RGB LEDs that need to be bent 90 degrees so they are pointing to the side of the circuit board so they can go into the holes in the plastic enclosure. The LEDs will only work if they are installed with the longer (positive) pin in the hole with the "+" sign on the circuit board! So we need to be careful when installing them. Also, don't push them all the way flush on the circuit board or you won't be able to bend them over. Instead, insert them until you feel some resistance from the wider, rough part of the leads, then bend them 90 degrees so the transparent package clears the end of the circuit board. Bend them with the leads inserted into the holes rather than before you insert them, it is easier to make them uniform this way.
You can insert and bend all 10 LEDs before you solder them on the other side, or do them one at a time, or in batches. But you will want them all at the same level and evenly spaced so they fit into the holes in the case - they may need to be bent a little after they are soldered to fit in the holes.
Step 7: Solder the Transistor Q1
The transistor Q1 helps amplify the audio signal from the microphone. It comes in a black D-shaped package with three leads. Align the flat side of the D toward the top of the board and insert the three leads in the holes - you may need to spread the wires slightly to get them to fit. Push the transistor in towards the board, which will spread out the leads on the back side. Then solder and clip the excess length. The leads are close together so be careful not to short out the leads with blobs of solder - check to make sure each lead is separated on the back side of the board.
Step 8: Solder the Microphone MK1
Now the taller components will be added to the board. The microphone has two pins that are offset from the center so pay attention to how the round component fits into the white circle on the board - reverse the leads if the microphone isn't centered on the circle. It is easier to do it this way than to figure out which of the pins is negative from the markings on the bottom.
Step 9: Solder capacitor C3
There are two capacitors that need to be soldered, they are electrical components that act like little batteries and store electric charge to filter out variations in a voltage signal. These capacitors have different values are polarized so they have to be inserted the correct way. The value of the capacitor is printed on the plastic shell, and C3 is the "1uF" value. There is a white stripe on the plastic shell that shows where the negative lead is, so make sure this gets installed away from the "+" sign printed on the circuit board.
Step 10: Solder LED11
There is an eleventh LED that is not installed in the row that are pointed towards the top of the board. Make sure the longer lead goes in the hole with the "+" label, but push the LED all the way against the circuit board rather than leaving space like you did earlier.
Step 11: Solder C2
The last component is another capacitor C2, with a value of 100 uF. Make sure to install it with the striped negative lead inserted away from the "+" mark on the circuit board like you did with C3.
That should be the last component to install on the circuit board since capacitor C1 seems to have gone missing.
We will solder power wires to the LED board and other components next week. Here is how the finished board should look:
Testing The LED Board
Once all the components have been soldered to the LED board it should be tested electrically. The board takes a 5 Volt power supply from wires that go to the holes marked J1 (but not jumper J1! Look for the rectangle in the lower right of the board.) We can attach test leads to an adjustible laboratory power supply and make contact with the round pads on the wiring side of the circuit board temporarily to test it.
Attach the pointed test probe wires to the jacks on the power supply and adjust the output voltage to 5.0 volts. Insert the pointed tips of the probes in the J1 holes from the bottom of the board, being careful to connect the red positive probe to the bottom "+" hole. Hold the tips in place and make noise for the microphone - the LEDs should flash in sequence and change colors if illuminated for a while. If your board has problems, talk to Tim for help with debugging.