This project is pretty easy, and should take about 20 minutes once you have everything ready, or up to about an hour if this is your first soldering project. Remember to review ALL the steps before you start doing the first step. It will probably take you longer to read them than it will to make it 🙂
The steps described are the basic, standalone steps. Some things to think about:
- Some components are optional, like the ISP, which you only need if you are going to reprogram.
- Are you going to have an Arduino be the brains? If so, you don’t need the MCU.
- You can also connect an Arduino to the reset pins instead of a switch.
- Are you going to power it from an Arduino? Then you don’t need the wUSB.
Note to rookies: If this is your first project, and you are stuck, send us an email and we will try to help you. Mention it is your first project!
Let’s get started!
We’re going to add all the components onto the board one at a time, starting with the passives (resistors and capacitors). Mount the empty DayCounter PCB into your Panavice Jr, other electronics vice or whatever you are using to gently hold it in place.
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First, we’re going to put the 16 470 ohm current limiting resistors in (they are the small ones, Yellow Violet Black). Mount the PCB into the Panavise with the silk screen facing upwards. The idea is to put the resistors in, keeping them in place with masking tape, so they don’t drop out when we turn the board over, then solder them. We’ll do one first, the the others all at once. | |
Bend the lead of the first resistor 90 degrees. Drop it tinto the holes as shown. Resistors can be inserted either way around. | |
Put some masking tape over it and turn the PCB over in the Panavise, and solder the leads on the other side. Then check the soldering worked well and the resistor is snug against the board. If not, you can reheat it and (using a cloth to protect you from the heat) re-melt the solder and push on it at the same time. | |
Great! You have one resistor in. We are going to do all the others using the same method. Bend the leads of each of the remaining 15 470ohm resistors, and drop them into the holes as shown. | |
Put some masking tape over all the resistors, making sure it is stuck down nicely. | |
Turn the board over and solder the leads. Notice how the solder is not placed directly on the iron, but rather against the pad/lead. You want the soldering iron to heat the lead and pad, and for the solder to flow towards the soldering iron. This prevents problem joints, which can be hard to track down. | |
Be systematic, working from one side to the other. If the leads you have already soldered are getting in the way, clip them off as you go. Once they are all done, remove the masking tape and check they all look neat. | |
Now we will do the small blue capacitors. Again, drop them in, hold the in place with masking tape. Turn the board over to solder them, and clip the leads. | |
Next is the 6-pin In System Programming (ISP) header, used for reprogramming the chip. This component is optional. This part has more then two pins, so we will use the rule: solder-1-pin-then-check. Once it looks good, solder the other pins.
As usual, stick it down with masking tape. Push the pins through the tape to get a nice stickdown. |
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Turn it over and solder one pin only. | |
Now remove the tape and take a look to make sure it is nice and flush against the board. If not, reheat the pin you soldered while pushing against the ISP header until it is flush. It will get hot, so use a cloth, a few layers of masking tape or something so you are not pushing with your bare fingers. You do not need to clip the leads. | |
Now drop in the 10 K-ohm “RR” pullup resistor (Brown-Black-Orange). This resistor keeps the reset pin high, preventing the chip from resetting if it still has power. It can be inserted either way round. Use the masking tape technique to keep it in place, turn the board over and solder it. Clip the leads. | |
Next, put in the crystal. It can be inserted either way around. Push it down flush, turn the board over and solder it. | |
Now it is time for the two 74HC595 shift registers – the bigger, 16 pin chips. These are one of my favorite chips, real workhorses.
To insert them, find a flat hard surface, and carefully bend all the pins on each side a tiny bit – about 0.1″. If you try and insert the chips without doing this, they won’t fit in the holes nicely. |
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Now insert them into the board. The dot on the top corresponds to pin 1, and should be on the same side as the notch on the silkscreen. This is VERY important.
Now hold them in place with masking tape, turn the board over and solder. Use the solder-1-pin-then-check method. If you are happy, solder all the other pins. You do not need to clip the leads. |
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Now insert the smaller 8-pin microcontroller chip. Again, the dot on the top should be on the same side as the notch in the silkscreen picture.
Hold it in place with masking tape, and use the solder-1-pin-then-check method. If you are happy, solder all the other pins. You do not need to clip the leads. |
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Almost there! Now solder in the USB breakout board. We will use the 4 pin header to connect the USB board to the main board. Put the boards on top of each other and drop the header in to keep them together. | |
As usual, stick some tape to hold it in place, and turn the board over. Use the solder-1-pin-then-check method. The solder all 4 pins on the underside of the board. | |
Now turn the board right side up, and remove the plastic holding the pins together. One good way is to work it out with tweezers or a screwdriver. Be careful not to damage the traces!
It can be easier to do this in your hands – this picture shows it mounted in the vice, but take if out if that works for you. Once it is off, solder the tops of the pins. |
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The final step is to solder the 7-segment display. This goes on the BACK of the board. It needs to go in the right way. Turn the board over in the vice.
The top right of the 7-segment is next to the 8-pins of the microcontroller, circled in red. Again use the solder-1-pin-then-check. Once you are happy, solder all the pins. |
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You can now test it out. We have one more step to do, which is to connect the wires and reset switch. How you do this depends on your particular application, so spend some time thinking about that before you do this. I’m going to show you what I did for the XKCD “reset” project. This will work for any installation inside a picture frame or project box. First, solder the switch between two pieces of wire stripped at both ends. New to switches? Solder one wire to each side of the blue line in this picture. |
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Now solder the one wire to each of the “reset” pads. It does not matter which way around they go. | |
You’re DONE. Congratulations! |
Plug it in, and away you go!