Ready to assemble your PETdisk kit? Here’s how to do it.
Gather the PETdisk components and your tools.
1 PETdisk board
1 vertical USB A connector
1 vertical USB B connector
2 1/8″ audio jacks
1 20 ohm resistor
4 3.3v zener diodes
1 2-pin vertical pin header
1 4-pin vertical pin header
1 7-pin right angle pin header
1 uSD adapter
1 7-pin inline socket (1/2 14 pin socket)
1 28 pin socket (for ATmega168)
1 programmed ATMega168 MCU
1 TL082 opamp
1 8 pin socket
1 12-position edge connector
1 6-position edge connector
“Save/Load” or “In/Out” label (not shown)
Confirm that your components match those in the picture. Contact me if anything is missing.
As far as tools required, you will need:
A soldering iron and solder. Any solder suitable for fine electronics work will do the job.
A sharp utility knife.
Pliers and wire cutters.
Optional, but useful – a multimeter and desoldering braid.
Now let’s continue on.
Separate the boards.
The PETdisk is composed of two pieces. One piece connects to the IEEE-488 port on your PET. The other connects to the cassette port, and serves as a power supply for the other board as well as allowing you to load/save cassette programs to a computer sound card. We need to separate the two board halves.
Once you have a deep, well defined cut on both sides of the board along the separator line, take a sheet of paper and fold several times. Cover the short end of the board with it and grip the board with a pair of pliers. Put the tip of the pliers close to the cut you made. Slowly bend the board along the cut line. The board should start to break evenly along the cut line. If you encounter resistance, go back and deepen the cut line on both sides and try again. Be gentle with the bending and don’t move quickly to avoid breaking the board unevenly.
With a bit of pressure the board should crack evenly along the cut line. Once the board has cracked, remove the pliers and paper and bend back and forth along the line by hand until the halves separate.
Your two halves are now separated. Lightly sand the rough edges of the separated boards with a fine sandpaper, until they are smooth. Now get your soldering iron heated up, because we are ready to start attaching the components.
Assemble the cassette interface board.
Now we’ll start building the cassette interface board. Look for the ‘bitfixer.com’ text on the board. It should be face up and to the right. Check that your board alignment matches the photo, then continue.
Add the 8-pin socket as shown in the photo. Make sure the notch for pin 1 faces to the left. The square pad on the board is pin 1. Insert the socket, then turn the board over and solder the pins to the board pads. With all soldering in this project, take your time and check as you go for solder bridges. A multimeter is useful for detecting conducting solder bridges. You can check for resistance between traces that look like they are connected. Remove excess solder with a desoldering braid if needed.
Add the vertical 2-pin header as shown. Solder the header pins to the board pads. A useful technique for this and other parts is to solder one pin to hold it in place, then reheat it while you adjust the part for vertical alignment. Then solder the other pin(s) in place.
Place a jumper on the 2-pin header. Then add the two 1/8″ audio jacks as shown. Solder the leads to the pads as usual. I’ll stop telling you to solder things in place now, it will be assumed from now on unless specifically mentioned otherwise.
Squeeze together the pairs of contacts on the 6-position edge connector, then slide the connector onto the board as shown. The contacts on the connector will straddle the board edge and slide over the rectangular pads. It may require a bit of working back and forth to get the connector on. The connector should be slid all the way onto the board until it is flush with the board edge. Make sure the pins line up evenly with the rectangular pads on the board on both sides, top and bottom. Then solder the pins on.
Once the connector is soldered, insert the 8-pin TL082 opamp chip into the socket. The notched end should face left as shown. Your kit will include a label which reads either “Load Save” or “In Out”. Cut the two words on the label apart. Label the left audio jack “Load” or “In”. The right audio jack should be labeled “Save” or “Out”.
The cassette interface board is now complete! You can test the functionality of this part now. Go to the PETdisk operation page and follow the instructions for testing the cassette board. If everything checks out, we’re ready to proceed.
Assembling the IEEE-488 board.
Now for assembly of the board which connects to the PET’s IEEE-488 port.
Insert the 28 pin socket as shown. Make sure the notched end of the socket faces up. The square pad on the board is pin 1, make sure this matches with the notched end of the socket. Confirm that your socketed board matches the image and solder the pins. Take care here, the spacing is a bit tight on the bottom so take your time and be on the lookout for solder bridges. Clean your soldering iron often.
Add the 7-pin single row socket as shown. The side of the socket with the higher edge should be facing into the board. Check that yours matches the photo. You may need to solder 1 pin, align by reheating/adjusting for vertical alignment, then soldering the rest of the pins.
Add the 4-pin vertical pin header as shown. From the bottom of the single row socket, skip the two small holes and then place your header. There will be two holes remaining below your 4-pin header, as pictured. Solder the pins.
Now to add the zener diodes. These are the small red components with one black stripe. Insert the first as shown. The lead connected to the end with the black stripe should go into the square pad on the board. This is the first hole towards the top of the board, between the 28-pin socket and the 7 pin socket. Check that yours matches the photo. Insert the diode until the part is flush with the board surface:
Now we’re done with the diodes. Get the 20 ohm resistor, the little blue one, and bend the leads down. Go back to those two holes we skipped before when inserting the diodes. Insert your resistor into those holes as shown. The resistor is too wide to fit flat against the board, so it will angle up as shown. Solder and trim.
Now get the square USB socket, and insert into the holes at the bottom of the board as shown. The flat side of the opening will face down, the angled end facing up. Once the connector is inserted and flush against the board, solder the leads.
Squeeze together the pairs of contacts on the edge connector, and slide it on to straddle the left side of the board as shown. Double (and triple) check to make sure you have the edge connector on the correct side – bitfixer text facing up and toward the top, edge connector on the left. If you want to be thorough, look at the back edge of the edge connector carefully, and you will see the pin numbering marked. Pin 1 should line up with the rectangular pad on the top of the board (same side as bitfixer.com text and other components), at the lower left corner (next to the usb socket). Although the connector could be flipped and it wouldn’t matter. Work the connector onto the board edge, it may take some back and forth motion. Once the connector is firmly flush against the board edge, check that all the pins line up with the rectangular pads on the board. Once you are happy with the alignment, solder the connectors to the rectangular pads. You don’t need much solder here, just enough to coat the connector somewhat and connect to the rectangular pads.
You are nearly done! Only one bit of soldering left to do – attaching the 7-pin right angle header to the micro-SD adapter. Get the adapter and align it as shown. We are going to add a bit of solder to the pad which is one up from the bottom. Find the pad which is slightly indented to the right, and move one pad up from there. Add a bit of solder to coat the pad as shown in the photo.
Get the 7-pin right angle header, and hold it by the longer end. Align it so the shorter, bent pins are lined up with the SD card pads as shown. The first pin should line up with the pad you just coated with solder. Each following pin should line up with its own pad. Check to make sure each pin intersects only one pad. Once your alignment is right, hold the header there and use your soldering iron with your other hand to heat up the first pin (on the soldered pad) while you hold it in place. In a few seconds the solder will melt and the header will stick to the card in the alignment you were holding it in. Be aware of heat and hold the header from the pin furthest from the one you are heating. Check that the alignment is right and each header pin lines up with one SD card pad. The two pads on the edges of the SD card will not have header pins, this is normal.
Once you are happy with the alignment, solder the remaining pins onto the pads on the SD adapter. Start with the pin furthest from the one you just heated, this will avoid the header heating up and moving around while you solder. Reheat and apply a bit of new solder to the pin you originally attached when you get to it, to make a good connection. Double check that each solder connection looks solid and reapply if it is necessary.
You are now done soldering! You can turn off your soldering iron now. Breathe some fresh air. Take the programmed ATMega8 microcontroller (the 28-pin chip) and insert it into the socket on the board. The notched end of the chip should face up. You may have to gently bend the pins to line up with the socket. Do this carefully to avoid bending or breaking any pins.
Take the SD adapter with pins that you just soldered, and insert into the 7-pin socket as shown. Check that all pins are lined up with the socket holes. The opening for the microSD card is facing up, and the side of the adapter with the cutout is facing away from the upper board edge. This should go in only one way, but double check that yours matches the picture.
Congratulations, you have completed building your PETdisk! You can apply the attractive bitfixer.com labels as shown, if you wish. Now go to the PETdisk operation page and test it out. Feel free to contact me with any questions. Now go load something onto your PET. Enjoy.