CB2 micro

Building guide

About this manual

This is the assembly manual for the CB2 micro. Follow the next instructions to assemble your CB2 micro.

Quick index reference

Click on a word in the table below to navigate to the relevant section of the manual. Then use "back" on your browser to return to this table.

1 CB2 micro information
1.1 Schematic diagram
1.2 PCB layout
1.3 Photo of the assembled CB2 micro
1.4 Components list

2 Before you begin the assembly
2.1 Requirement tools
2.2 Soldering instructions
2.3 Health and safety
2.4 Unpack the components
2.5 Inspect the components

3 Assembly procedure
3.1 Step 1 - Solder the crystal
3.2 Step 2 - Solder the chip
3.3 Step 3 - Solder the crystal capacitors
3.4 Step 4 - Solder the rest of the ceramic capacitors
3.5 Step 5 - Solder the mini USB connector
3.6 Step 6 - Solder the diodes
3.7 Step 7 - Solder the electrolytic capacitors
3.8 Step 8 - Solder the transistor and the resistors
3.9 Step 9 - Solder the serial and PS/2 connectors
3.10 Step 10 - Solder the SCART connector
3.11 Step 11 - Clean the PCB

4 Initial power up
4.1 Set the PAL/NTSC jumper
4.2 Connect the keyboard
4.3 Connect the TV
4.4 Connect the power
4.5 Boot up the micro

5 Troubleshooting

1 CB2 micro information

Following are important information that will help you assemble and debug your CB2 micro.

1.1 Schematic diagram

Below is the complete schematic of the CB2 micro. Click on the image for a bigger resolution schematic.

1.2 PCB layout

Below is the PCB layout of the CB2 micro, including the components positions.

1.3 Photo of the assembled CB2 micro

Below is a photo of the fully assembled CB2 micro. Click on the image for a bigger resolution. Note, in the picture, jumpers J2/J3-J4/J5 have not been fitted in place. You should fit either J2/J3 or J4/J5 depending on your serial cable and serial connection required. Use a short piece of a cut component lead to short out the jumpers. The rest of the PCB is shown completely assembled.

1.4 Components list

Here is the components list for the CB2 micro. For your convenience, the components appear in the order they are soldered onto the PCB. Also, this list includes a check box field that you could mark as you solder each component onto the PCB. You should use this list along with the assembly procedure to assemble your CB2 micro.

Component Label (on schematic)	Component Value	Info/Markings/Codes onto component	Component Photo	Soldered component photo	Soldered?
-	CB2 micro PCB	CB2 micro * Note, since 2023, some purple PCBs are also available.		-	-
X1	20MHz	20.000
IC1	ATMEGA644P	ATMEGA644P-20PU or ATMEGA644PA-PU
C3	22pF	22
C4	22pF	22
C2	100nF	104
C5	100nF	104
C6	100nF	104
C7	100nF	104
Mini USB	Mini USB connector	Small metal connector * Note, since 2022, the connector comes mounted on the PCB, but you have to solder its pins.
D1	BAT85	BAT85
D2	BAT85	BAT85
D3	BAT85	BAT85
D4	BAT85	BAT85
C1	33uF	33uF * Note, since 2022, the capacitor provided is longer.
C8	33uF	33uF * Note, since 2022, the capacitor provided is longer.
T2	2N2907	2N2907
R1	1k	brown, black, red, gold * Note, since 2022, a blue resistor is supplied.
R2	1k	brown, black, red, gold * Note, since 2022, a blue resistor is supplied.
R3	1k	brown, black, red, gold * Note, since 2022, a blue resistor is supplied.
R6	1k	brown, black, red, gold * Note, since 2022, a blue resistor is supplied.
R7	1k	brown, black, red, gold * Note, since 2022, a blue resistor is supplied.
R11	1k	brown, black, red, gold * Note, since 2022, a blue resistor is supplied.
R12	1k	brown, black, red, gold * Note, since 2022, a blue resistor is supplied.
R13	1k	brown, black, red, gold * Note, since 2022, a blue resistor is supplied.
R14	1k	brown, black, red, gold * Note, since 2022, a blue resistor is supplied.
R18	1k	brown, black, red, gold * Note, since 2022, a blue resistor is supplied.
R4	6.8k	blue, gray, red, gold
R5	6.8k	blue, gray, red, gold
R15	6.8k	blue, gray, red, gold
R8	470 ohm	yellow, violet, brown, gold
R9	470 ohm	yellow, violet, brown, gold
R10	470 ohm	yellow, violet, brown, gold
R16	3.3k	orange, orange, red, gold
R17	1.8k	brown, gray, red, gold
R19	180 ohm	brown, gray, brown, gold
Sub-D 9 (f)	Dsub-9 male connector	Big black plastic-metal connector
PS2 (f) front	PS/2 female connector	Big metal connector. * Note, since 2022, a black connector is supplied.
SCART (f)	SCART female connector	Big plastic connector. * Note, since 10 Mar 2023, a black connector is supplied.

2 Before you begin the assembly

If you are a beginner in soldering, take some time to read the information below, before you start soldering the CB2 micro. If you are an experienced builder, you may choose to skip some sections, but it is recommended not to, so as to avoid problems associated with the assembly of the CB2 micro.

2.1 Requirement tools

The tools required to assemble the CB2 micro are:

A soldering iron, prefferably one with adjustable temperature range.
Solder with embedded flux in it, prefferably lead-free solder.
Brass sponge or damp sponge for cleaning the tip of your iron.
Cutter, for cutting off the components leads.
A small magnifying lens, for inspecting the solder joints or identifying components, especially if your vision is poor.
Acetone without oil or perfume in it, or other PCB flux cleaning chemical, for cleaning the soldered PC.
A small piece of cotton wool or alternatively an old toothbrush, for wetting the acetone to it.

2.2 Soldering instructions

Simple step by step guide to soldering

1. Place the component into the board, making sure it goes in the right way around and the part sits flush against the board. Watch out the chip, the diodes, the transistor and the electrolytic capacitors orientation!
2. If needed, bend the legs very slightly to secure the part. Flip the board so you can access the pads with a soldering iron.

3. Make sure the soldering iron has warmed up. If necessary, before each component leg soldering, use a brass soldering iron cleaner or damp sponge to clean the tip.

4. Pick up the Soldering Iron in one hand, and the solder in the other hand.

5. Place soldering iron tip on the pad.

6. Feed a small amount of solder into the joint. The solder should melt on the pad and flow around the component leg.

7. After 3 to 5 seconds, remove the solder, then remove the soldering iron.

8. Leave the joint to cool for a few seconds, then using a pair of cutters trim the excess component lead.

Examples of good and bad solder Joints

The appearance of a solder joint tells a lot about how good it is. A good solder joint is shiny. This means that the solder has not been overheated and exhausted the flux contained in it. There must be enough solder to form a nice fillet, without excessive solder bulging out. The component leg should be ideally in the centre of the joint. This photo shows an ideal solder joint.

The following illustrates an acceptable solder joint. The solder is shiny, but there is slightly more solder than required, and the component leg is off centre.

It can be tricky to add just the correct amount of solder and heat time when learning. The following photo shows a typical joint with not enough solder. The component hole is not covered. It is possible this joint will work, but it will probably fail quickly.

Slightly too much solder causes a bulge, as illustrated in the following photo.

The PCB tracks are covered in a special paint called solder resist or solder mask. This helps prevent the solder from flowing away from the joint. As more solder is added it builds into a blob, as shown in the next 2 photos.

Too much solder on a joint can cause bridging to adjacent components, leading to a short circuit.

Solder contains flux to ensure the joints are good and not oxidised. The flux works by reacting with the oxides that are present, and converting them back to metals. Overheating the joint, by leaving the iron too much time onto it, can use all the available flux. This leads to the solder oxidising and what is known as a dry joint. The following joints are also 'Dry'. Note that a dry joint does not necessarily mean that it does not have enough solder, but refers to the solder not 'wetting' the component and the pad correctly to flow.

Notice the 'Orange Peel; roughness of the solder. This is caused by the metal in the solder turning to oxides. Compare this dry joint which has too little solder, to the next one which has too much solder – notice the comparatively dull appearance of the solder on the dry joint.

Overheating a solder pad on a PCB can also cause the copper layer to come away from the fibre glass that the board is made from. This can cause circuit failure when the track on the circuit board breaks, leading to an open circuit.

2.3 Health and safety

Lead-based solder
The CB2 micro has lead-containing parts. The use of thin gloves is recommended when building the CB2 micro. If you find it too difficult to solder with the gloves on, you may not use them, although recommended. If you do not use gloves, take care not to put your hands on your clothes, in your face and especially in your nose, eyes, ears or mouth after you have touched the PCB or when soldering. Lead is a toxic metal that easily sticks on your hands even on small quantities without noticing. Whatever you do, make sure you never put your fingers in your mouth or nose and eyes, as lead must not find a way into your body at any case. To minimize lead contamination do not do anything else while you are soldering the CB2 micro. You should not touch your house door knobs, you should not drink or eat or smoke, or have kids and other people near by. You could allow kids only to watch, without touching anything, provided that there is a good ventilation in the room (open windows).

The CB2 micro components contain low amounts of lead-based solder on them, but the greatest source of lead contamination will be your lead-based solder if you use one. This solder is the most likely source of lead contamination, so make sure you follow the instructions in these paragraphs when assembling your CB2 micro. After you finish soldering throw away the gloves you may have used. If you have not used any gloves, then go to the sink, without touching any house door knobs, surfaces etc. and wash your hands for good with soap for two or three times, rubbing them well. This will ensure that your hands are clean of any lead contamination.

If you have the ability, it is recommended you use lead-free solder to build the CB2 micro, even if the components contain lead-based solder. Using lead-free solder alone will expose you in far fewer amounts of lead. After finishing the CB2 micro assembly, make sure you clean up the workbench. Do not use the house vaccuum cleaner at any instance to suck in the tiny bits of solder and there is a reason for not doing so. Use lightly wet handkerchiefs to make the tiny solder bits stick into them and and throw them away after cleaning.

It is also recommended to enclose your CB2 micro into a suitable enclosure, to limit the lead exposure in the future, from touching the assembled PCB. A lead-containing project that is completed and enclosed in an enclosure do not harm, but a PCB soldered with lead-based solder and hanging around your workbench without an enclosure, will eventually cause lead contamination problems.

Solder fumes
Avoid breathing the solder smoke when building the CB2 micro. Open the room windows if that is possible, if you don't have a ventilation system. You may also place a small fan to suck the smoke away from the area you solder. The fan shoud blow the smoke away from you, not towards you. Whatever you decide to do, the idea is to move the solder smoke away from your face and take it outside the house somehow. It is not only the resign that evaporates that might cause problems, but also microscopic metal particles from the solder, that may be eventually released into the air, although this last part is very ambiguous.

Eye protection
You never know when melted solder, hot resign droplets or even the soldering iron tip will end up onto your eyes. Also, any liquid cleaning chemical may eventually accidentally thrown onto your eyes. So wear protective glasses when you build the CB2 micro. If you do not have any, wear at least your ordinary glasses, if you happen to have. Doing a small mistake or ignoring the danger, can seriously harm your eyes, or make you totally blind at worst case. Does it worth it? Do not say "I am careful, it won't happen to me", eventually it may! Listen to people with previous experience on this.

Disclaimer
I am not responsible about any damage to your health or property, if you decide to follow or not the above recommendations when assembling and using your CB2 micro. These are my recommendations, after years of experience in soldering, both with care and also careless. Do not be scared about these things too much however, build your CB2 micro and enjoy it. But, following these simple recommendations will ensure a much safer way for you and the other's nearby when assembling it.

2.4 Unpack the components

When you receive your CB2 micro, unpack the components carefully, making sure not to forget any component inside the shipping box/folder. Place the components inside a small box, so that you avoid losing any of them during the CB2 micro assembly. It is important to make some clear space on your bench, to help you see and organize the components better. If you do not assemble your CB2 micro onto a lab bench, but onto a table used by other people for other purposes, make sure you place a protective cover to that table, for avoiding contaminating it with lead.

2.5 Inspect the components

After you have all the CB2 micro components placed onto your bench, inspect each of them carefully with the help of a magnifying glass for visible signs of damage. Damaged components may be able to be fixed (for example chip bent pins due to postage) or not (for example a broken resistor). In the later case, the component has to be replaced prior to soldering it onto the PCB.

3 Assembly procedure

Follow carefully the steps below, to assemble your CB2 micro. If you closely follow this procedure you will ensure an easy build and the assembled board will contain no errors. For the assembly procedure make sure you have seen the components list, as this will be very useful during the CB2 micro assembly process.

The PCB that you receive with your CB2 micro, has markings for each component value instead of the component label. This way, if you have basic soldering and components identification skills, you can assemble the CB2 micro without even looking at the components list.

All the components of the CB2 micro are soldered from the bottom side of the PCB only. The only exception is the body of the mini USB connector, which has to be soldered from the top side of the PCB as well. All the PCB pads (except those of the crystal) are through hole, so you do not need to fill them with solder all the way up to the top side of the PCB.

3.1 Step 1 - Solder the crystal

Solder the crystal as illustrated below.

The crystal has no polarity, so you can solder it any way you like.

3.2 Step 2 - Solder the chip

Before you solder the chip you have to bend its pins a bit inwards, so that it can fit to the PCB pads. To do this, hold the chip black rectangle body from the sides (where there are no pins), using the fingers of your both hands and make sure you do not touch the chip pins with your fingers. Then place each side of the pins on a flat surface. Then push each side against this flat surface until the pin row on that side bends just about right (perpendicular to the chip body, not too outwards and not too inwards). If the pin rows at both sides of the chip have been bent correctly, the chip should slip into the PCB pads easily.

Take great care of the orientation of the chip before you solder it onto the PCB. If you solder it the wrong way, you could not correct this afterwards. The correct soldering way is illustrated below. Note the chip dot shown by the red arrow.

Below, the crystal and the chip is shown soldered onto the PCB. This is how the chip should be soldered.

3.3 Step 3 - Solder the crystal capacitors

The two little 22pF ceramic capacitors should be soldered next.

The picture below, illustrates the soldered capacitors.

3.4 Step 4 - Solder the rest of the ceramic capacitors

The rest of the ceramic capacitors, all 100nF, should be soldered next.

The picture below, illustrates the soldered capacitors.

3.5 Step 5 - Solder the mini USB connector

The mini USB connector is the next component to be soldered. This is a bit special because you need to solder the metal body this component from both sides of the PCB, the bottom and the top. This is optional however and if you are afraid of overheating the connector, you may solder it only from the bottom.

Press the connector with your fingers firmly, to fit it into the PCB and solder it's five pins carefully on the bottom side of the PCB. The pins are close enough, so care must be taken not to short circuit these pins. You may use a multimeter (continuity tester) after you have soldered these pins, to ensure that there is no short circuit between them.

The metal body of the connector, cannot be easily soldered from the bottom side of the PCB because it's pins are short, so this has to be soldered from the top as well (again, this is optional however and if you are afraid of overheating the connector, you may solder it only from the bottom). To do this, fit a mini USB cable to the connector and then increase the temperature of your soldering iron to about 360C. Then solder the connector metal body from the top side of the PCB pads. Do not leave the soldering iron too much onto the connector, to avoid melting it's plastic parts. After each pad is soldered, blow the connector with forced air, so that it cools down rapidly. Then repead the procedure to the other pad. The purpose of having the mini USB cable plugged into the connector when soldering it, is to keep the internal pins correctly alligned, in case the connector plastic is misaligned from excessive heat.
The pictures below, illustrate the soldered mini USB connector, shown from both sides of the PCB.

3.6 Step 6 - Solder the diodes

The four diodes should be soldered next.

Make sure the diodes are placed onto the PCB with the correct orientation. The little black line on one side of each diode, must match the thick white line of the diode component onto the PCB.

3.7 Step 7 - Solder the electrolytic capacitors

The two 33uF electrolytic capacitors, should be soldered next.

Make sure you solder these capacitors in the correct orientation. The pictures above, illustrate the correct orientation of both the capacitors. Note the red arrows pointing to the gold thick lines onto the bodies of the capacitors.
The picture below, illustrates the soldered diodes and capacitors, also showing their correct orientation.

3.8 Step 8 - Solder the transistor and the resistors

The transistor is the next component to be soldered. It's correct body orientation matches the component markings onto the PCB and it is also illustrated in the next picture.

Next, all the CB2 micro resistors should be soldered. In the CB2 micro, all the resistors are soldered vertically onto the PCB. Although they have no orientation, it will be more neat to fit them as illustrated onto the PCB resistor markings. Just bend one of the resistor pins and fit it into place, then solder it. Make sure the resistor exposed pins are not touch to near by components.

The picture below, illustrates the soldered transistor and resistors.

3.9 Step 9 - Solder the serial and PS/2 connectors

The serial and the PS/2 connectors, should be soldered next. The serial connector requires quite a big amount of solder to it's big side pins. Increase the temperature of your iron to about 360C and quickly fill the big holes of these pins with solder. Make sure the excess solder does not drop on the other side of the PCB though. After each pad is soldered, blow the connector with forced air, so that it cools down rapidly. Then repead the procedure to the other pad.

The PS/2 connector also requires quite a big amount of solder to it's three big pins. Increase the temperature of your iron to about 360C and quickly fill the big holes of these pins with solder. After each pad is soldered, blow the connector with forced air, so that it cools down rapidly. Then repead the procedure to the other pads.

The picture below, illustrates the soldered connectors.

3.10 Step 10 - Solder the SCART connector

The big SCART connector is the final component to be soldered. This component requires quite a bit of force so as to be secured onto the PCB prior to soldering. Notice the two big elastic plastic side springs of the connector, that have to clip firmply onto the PCB holes. Also notice the little plastic guides under the connector, that have to fit into the smaller PCB holes.

Align the connector pins properly onto the PCB pads and push the connector firmly until the two side springs clip into the PCB pads. You may need to manually help the bending of these springs by pushing them inwards with your fingers so that they enter the PCB holes easier. When the connector is secured in place, solder the connector pins. After soldering the connector you may want to cut the excessive plastic springs from the bottom of the PCB. In that case, take care not to cut them too much and weaken their clip action.
The soldered connector is illustrated in the picture below.

3.11 Step 11 - Clean the PCB

The final step is to clean up the bottom of the soldered PCB with acetone or any other suitable PCB flux cleaning chemical. This is recommended even if you use "no-clean" solder flux. If you use acetone, make sure it has no oil in it or perfumes. Pour quite a few drops of acetone onto a cotton wool and start cleaning the excessive flux from the bottom of the PCB only. You may have to repeat this process lots of times using a fresh piece of cotton wool and acetone until the result is satisfying and the PCB is clean of flux. After the acetone is dried from the PCB, clean the pieces of remaining cotton wool from it. Alternatively, you may use an old toothbrush instead of the cotton wool. Just make sure you won't use this toothbrush to brush your teeth afterwards, no matter if you wash it well.

4 Initial power up

4.1 Set the PAL/NTSC jumper

After you have successfully assembled your CB2 micro, make sure you have set the J1 (PAL/NTSC) correctly. J1 must be open when PAL is used and shorted on NTSC. Use a short piece of a cut component lead to short out the jumper on NTSC.

4.2 Connect the keyboard

The next step is to connect a PS/2 keyboard to the micro. Note that you can use a USB keyboard along with a USB to PS/2 adaptor, provided that your USB keyboard is compatible with the PS/2 port. In other words, your USB keyboard must have the electronics inside to support the PS/2 port, otherwise it won't work, as the USB to PS/2 adapter has only a passive wiring into it.

4.3 Connect the TV

The next step is to connect the CB2 micro with a SCART cable to your TV. Note that, if upon powering up of the micro, there is no signal on the TV, try to use the other available scart connector input in the TV, if there is one. In case your TV is black and white or if it has only a composite video input, you can connect the CB2 micro directly to the composite video input of the TV, from the "B/W out" pad onto the PCB. Of course this provides only a gray scale composite signal. Alternatively, for color composite video, you can use the SCART connector on the CB2 micro, along with a commercial SCART to color composite video/audio adapter. If you do not want to buy a commercial adapter, you may consider building this simple adapter yourself, to convert the H-sync, V-sync and the RGB signals from the SCART connector on the CB2 to color composite video or S-video. Similar things apply to audio too. The audio pad on the PCB of the CB2 micro is marked as "AF out". If you use the SCART connection, there is no need for a separate audio connection to the TV.

Connecting the CB2 micro with HDMI TVs or VGA monitors is only possible with the use of external adapters. These adapters usually cost less than 10$ so they are very affordable in case you do not have a SCART-featured TV.

4.4 Connect the power

The next step is to connect a USB to miniUSB cable to the miniUSB port of the CB2 micro. The USB side of this cable can be connected to any USB device port, such as the USB port of a PC, the USB port of a smart TV, the USB port of your mobile phone charger, the USB port of a power bank or any other USB device that is capable of providing power to the USB port. Only the power pins of the USB connector are used, so you do not need to worry about the data pins.

You can also power up the CB2 micro from an ordinary 5V regulated power supply, by soldering the power supply cables to the corresponding 5v and GND PCB pads. It is important that the power supply is regulated, to avoid damaging the CB2 micro. In that case it is also important to remove any USB cable connected to the miniUSB port of the computer, so as to avoid damaging the USB ports of the external devices connected to the micro. Note however, that there could be cases where you may want to use the miniUSB port of the CB2 micro to power up other external devices, such as measurement equipment. It is up to you to decide how to use the power scheme, so have in mind that the miniUSB and the 5V pad on the PCB are connected directly, so each of them can be used as power input or output.

4.5 Boot up the micro

The CB2 micro, comes with a pre-programmed chip so that it is ready to be used. Provided that you have successfully assembled the CB2 micro according to the instructions and you have connected all the cables to it (SCART, PS/2, miniUSB or regulated PSU), when you first power it up, an intro screen appears for a few seconds and then the main menu area appears. The main menu area is comparable to the desktop of a PC and contains, among others, the 8 program slots. These slots are positions where you can store your programs. The BC2 micro, comes with a pre-programmed chip and the 8 program slots are pre-filled with different programs and games that you can try right away. You may erase any of them and write your own BASIC programs. You should read the user manual to get started with the CB2 micro.

5 Troubleshooting

Provided that you have assembled your CB2 micro according to the exact procedure and instructions presented on this page and that you have connected all the cables correctly to it (SCART, PS/2, miniUSB or regulated PSU), there are not many things that can go wrong. In the event that the CB2 micro refuses to show a signal on your TV, try out another SCART connector on your TV, if there are two or more of them and set the TV accordingly. If you have no success, use a multimeter and check the voltage on pins 10 and 30 of the chip, which should be 5v. If it is not 0v, check your USB power adaptor or power bank if you use one, or check the PCB for shorts using the continuity tester of the multimeter, after you remove the power from the CB2 micro. If it is 5v, then read again the procedure in this page and make sure you have performed all the assembly steps accordingly. If you still can't find the problem, you may contact me for support, which I will be happy to provide in the context of the available time.