S-AVR » LED
The S-AVR:LED is a small bit of veroboard which will display the 8-bit value of a port on eight LEDs. It uses eight transistors as switches, because the MCU ports are unable to supply sufficient current to drive a LED at acceptable brightness. The board itself is just eight copies of the circuit shown here:
Step 1: Tool-Check
You will need:
- S-AVR
- Soldering Iron & Solder
- Sharp Knife or Scalpel
- Wire Cutters/Strippers
- Long-nose pliars
Step 2: Order the Components
You will need the following components. For readers in the UK I have included the order codes for Rapid Electronics. If you're elsewhere it probably makes sense to source the components locally - they are very common and should be easy to find. Note that if you have already made the S-AVR main board, you probably have enough stuff left over to meet the last three items in the list. If not, the complete order from Rapid comes to £6.69. Then you pay delivery at £4.95 and VAT on that total, bringing it up to £13.37. Rapid will give you free delivery for orders over £30 ex VAT, so if you're short of common components it probably makes sense to stock up of a few things. You will get discounts for ordering more than five or ten.
| Rapid Order Code | Description | Quantity |
|---|---|---|
| 55-0155 | 5mm Red LED | 8 |
| 47-5538 | BC637 NPN Transistor | 8 |
| 63-2340 | 4K7 1/4W Resistor | 8 |
| 63-2325 | 360R 1/4W Resistor | 8 |
| 22-1703 | 32-Way Turned-Pin SIL Socket | 1 |
| 01-0102 | Single-Core Wire | 1 |
| 34-0505 | 64mm x 95mm Stripboard | 1 |
Step 3: Cut the Tracks!
You know the drill by now. Cut the tracks where you see white lines.
Step 4: Solder the Jumper Wires
There is only one blue line this time. It represents a branch of the +5V line, so (confusingly enough) you should use a red wire. As before, the wire should be inserted from the other side of the board.
Step 5: Solder the Components
Note that components should be inserted from the other side of the board.
- Solder the 360R resistors and the transistors, using the orientation shown on the right. Note that the right-hand leg of each resistor shares a hole with its transistor's collector ("C"). Also, if you bend each transistor's emitter ("E") leg to the right, you will be able to make the connection to ground, as shown (e.g the red line between P8 and Q8). Do not yet solder the resistors' left legs.
- Resistor between C8 and O8, transistor at O8, O7 and P8
- Resistor between C11 and N11, transistor at N11, N10 and O11
- Resistor between C14 and M14, transistor at M14, M13 and N14
- Resistor between C17 and L17, transistor at L17, L16 and M17
- Resistor between C20 and K20, transistor at K20, K19 and L20
- Resistor between C23 and J23, transistor at J23, J22 and K23
- Resistor between C26 and I26, transistor at I26, I25 and J26
- Resistor between C29 and H29, transistor at H29, H28 and I29
- Solder the eight LEDs, with their long legs in column A. Bend each short leg to the right and solder to each 360R resistor's unsoldered left leg.
- Between A8 and B8.
- Between A11 and B11.
- Between A14 and B14.
- Between A17 and B17.
- Between A20 and B20.
- Between A23 and B23.
- Between A26 and B26.
- Between A29 and B29.
- Solder the eight 4K7 resistors:
- Between H2 and H5.
- Between I2 and I5.
- Between J2 and J5.
- Between K2 and K5.
- Between L2 and L5.
- Between M2 and M5.
- Between N2 and N5.
- Between O2 and O5.
- Solder 10 pins from the SIL strip between H1 and Q1.
Step 6: Connect it up!
Now place the completed LED board next to the S-AVR such that the LED board's SIL strip lines up with port A of the S-AVR. Make sure the power is off. Now take eight staples and insert them so as to bridge the two boards together. Finally use a 4cm length of black wire to bridge the S-AVR's ground line over to the LED board, and bridge the +5v line similarly with a 4cm length of red wire.
If you power the S-AVR on now, you will see the counter you programmed into it previously operating. The LEDs display the state of port A, which increments every second.
