Sunday, 29 December 2013

Building the Raspberry Pi Wobbulator Kit - Part 1

I took delivery of the the Raspberry Pi Wobbulator PCBs a few days ago and I've put a kit of components together to go with the PCB. The PCB is priced at £12.00, and the PCB plus kit of components is priced at £40. This includes all sales taxes and free worldwide delivery. The PCBs and kits are available here if you are interested. You can purchase online and pay by credit or debit card, or PayPal.

 The Raspberry Pi Wobbulator PCB is shown above. Assembly is fairly straight forward, but in this blog post and the next I'll go the assembly step-by-step and highlight any potential problems. This blog post deals with the surface mount components. I assume you have had some experience of soldering surface mount components, but in any case you will need a fine tipped temperature controlled soldering iron, some small diameter solder (0.5mm or smaller), a pair of tweezers and some kind of magnifier. I use a head mounted magnifier which leaves both hands free, but a good illuminated magnifier lamp would also be suitable.

Start off by soldering on the five 1 nF capacitors, C1 to C5 in place. Their positions are clearly marked on the PCB and it doesn't matter what was round they are soldered. These surface mount capacitors do not have their value marked on them, so it is important not to get them mixed up with other value capacitors! So please only work with one value of capacitors at any given time. The following photo shows the PCB with capacitors C1 to C5 soldered in place.

Next, solder the five 100 nF capacitors, C6 to C10 in place. Your PCB should now look the same as shown in the following photo.

Next, solder the five resistors R1 to R5 in place. Unlike the capacitors, the resistors do have their value marked on them in the form of a three digit number. The first two digits represent the value, and the third digit is the multiplier. So, for example, the 56 Ohm resistor R1 is marked "560", which means "56 followed by 0 zeros", in other words, "56". R2 is marked "105" which means "10 followed by 5 zeros", in other words 1000000 Ohms, or 1 M Ohm. Similarly R3 is marked "222", R4 is marked "470" and R5 is marked "103". The following photo shows the PCB with all five resistors in place

Next it's the turn of the discrete semiconductors. There is one transistor U1, and two diodes D1 and D2. The direction in which the diodes are soldered in place is important - they are marked (all be it very faintly) with a line at one end, and this corresponds to the line on the diode symbol. A closeup view of D1 is shown below - you can just about make out the line on the left-hand end of the component.

The following photo shows the PCB with the discrete semiconductors in place.

Finally, it's time to solder the ICs in place. Both ICs are Narrow Body Standard Small Outline Package format, or SOIC_N for short. I soldered them in place by first melting a small amount of solder on each pad on the PCB and then placing the IC in position and carefully pressing each "leg" down with the tip of the soldering iron until the solder melted and attached to the leg. Use whatever method works for you! The following photo shows the PCB with the IC's in position.

Congratulations! That's all the surface mount components in place - time to lie down in a darkened room until your eyesight recovers and your hands stop shaking... hi hi!

My next blog post will deal with soldering the remaining (through hole) components in place.


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  2. Hi Tom:
    I have building the wobbulator, no problem with the assembly, however I can't get the VR2 voltage to the required number the highest I could get was about .4 volts I checked the placement of the parts and soldering all ok. Need help
    Thanks Ross Bell K7RSB