 |
 |
 |
|
|
|
|
SMD-PB3 |
|
|
||
|
||
|
|
| - NEW - SMD-PB3: Surface
|
|
 (Order Kit from Products page) |
|
Full Kit Features: 131 components, includes spares 8 functrional circuits- can be asseblbed whole or separated Convienent, color coded card-pack keeps components organized |
|
| - Purpose | |
| With electronic devices getting smaller and more compact, individual electronic components are also getting smaller. New techniques are required to use them when bread boarding prototypes and building final assemblies. The purpose of this kit is to provide an economical and thorough means to practice and test surface mount device (SMD) assembly and soldering techniques. The kit does not contain specific instructions on how to assemble it because there are so many different methods: fine tipped soldering iron, hot-air soldering, hotplate/griddle, and toaster oven to name a few. To this end, the kit provides for the assembling of real components in a compact format to create real, functional circuits instead of soldering dummy components. If dummy components are over heated how would you know? If real parts are over heated, they do not work and you know you need to change your process. Mistakes can be made and learned from without any great loss, and then corrections can be tried on the next section. To allow testing of different techniques the board's circuits can be cut apart and assembled and operated separately.
|
|
| - Summary | |
|
The Surface Mount Practice Kit comes in two forms- the full kit (SMD-PB3-10) and half kit (SMD-PB3-05). The full kit consists of 131 components to create 8 circuits: two 4-bit ring counters and six astable flip-flops, driving a total of twenty LEDs. The half kit consists of 68 components to create four circuits: one 4-bit ring counters and three astable flip-flops, driving a total of ten LEDs. Though a better light display could be made using 1-of-10 decoded counters or a microcomputer chip, the point of the kit is to provide SMD Soldering practice. For this reason the board’s 8 circuits can be cut apart and assembled and operated separately. This allows testing of different SMD soldering techniques.
Inexpensive components where selected for the kit so there should be no fear of destroying “valuable” parts. Extra components are included to replace those that might get damaged or lost. Handling them will also require practice- When one slips out of the too-tight grip of a pair of tweezers, the tiny part can be catapulted into oblivion. “Good judgment comes from experience, and experience comes from bad judgment.” The part sizes selected for this kit are considered ‘large’ for SMDs- if you can call .120” ‘large’. This was done to make introduction to these new assembly techniques and processes as easy as possible. Once you have some experience and a process to assemble 1206 size components, it is not difficult to work with smaller parts. Even if only these ‘larger’ components are used for your new designs, a substantial reduction of PC board size will be achieved. A total of six flip-flop circuits (three in the half kit) provide placement and soldering practice with simple 2 and 3 terminal components- resistors, capacitors, LEDs and transistors. By building these circuit sections first, confidence is gained to tackle soldering the ICs in the ring counter circuits. If the board is kept whole, it can still be built one section at a time starting with the simple ten component flip-flops, and working up to the 14 pin ICs in the walking ring counters. The whole board with twenty flashing LEDs makes a nice attention getting display and an impressive light show in a darkened room.
|
|
| -Warnings - | |
|
Protect your eyes- Component damage due to thermal shock-
Monolithic multi layer ceramic capacitors are sensitive due to their layered construction; not only do the metal and ceramic layers have different rates of thermal expansion, but different thermal conductivity. Thermal shock can cause them to crack internally, reducing their capacitance and/or occasionally causing shorts. They can be soldered with a soldering iron, but care should be taken to use low wattage and temperature, and not touch the capacitor’s terminals directly with the iron, but only with the molten solder. The most reliable way is to slowly preheat them to about 280º F and then solder. Transistors and ICs are a little less sensitive to sudden thermal changes than ceramic capacitors. Care must be taken not to heat them above 500º F as this will damage the actual semiconductor material- the dopant elements will diffuse across the P-N junctions destroying them. Another problem that can occur is caused by absorbed moisture. This is most often a bigger problem with LEDs. Most SMD LEDs are shipped in a sealed moisture proof pouch, with a warning label recommending that the parts be baked-out to remove any absorbed moisture before IR or vapor phase soldering. If a SMD LED (or IC, or transistor) has absorbed moisture and is heated too suddenly, the water may turn to steam so quickly that it pops or ruptures the chip destroying it. This is another good reason to slowly pre-heat the parts and PC board before soldering. The kit’s parts are sealed in a heavy poly bag with a desiccator pack. It is advised that you do not open the bag until you are ready to solder. This will help prevent moisture problems. Component damage due to static electric discharge- |
|
| - Theory of Operation | |
|
The board consists of two types of circuits: a simple two transistor flip-flop that alternately blinks two LEDs, and a four-bit ring-counter that sequentially turns on, then off, the four LEDs. The Astable Flip-Flop Circuit: The flip-flop circuit can be in only one of two stable states- Q1 on and Q2 off, or the reverse. When Q1 is on, LED-1 is on, and when Q2 is on LED-2 is on. However, when ever Q1 is on, its collector (3) will be at Vcc, and capacitor C1 will discharge through R3, blocking current from flowing through Q2’s base. This keeps Q2 turned off, and quickly charges C2 from Q1’s base through LED-2 and R4. C1 will eventually finish discharging through R3 and base current will start to flow through Q2’s base (1) again. As soon as Q2 starts conducting, it raises the negative terminal of C2 to Vcc, and causes it to discharge through R1, blocking Q1’s base current and turning it off. This now recharges C1, and the cycle repeats causing the LEDs to alternately blink. The on/off time is determined by the values of R1,C1 and R3,C2. The Ring-Counter Circuit:
The ring counter consists of four clocked D-flip-flops (composed of two CD4013 dual D-flip-flop ICs) connected as a 4-bit shift register with its inverted ‘Q’ output connected back to the ‘D’ input of the first stage. (The D-flip-flop latches the value from the ‘D’ input on the rising edge of the clock signal and outputs it to the true and inverted ‘Q’ outputs.) Q3 and Q4 form an astable flip-flop to provide this clock signal. There is no LED on Q3 so it will provide a cleaner clock signal. When the circuit is first powered up, C4 holds the reset line (labeled ‘R’) high to set the initial state of the D-flip-flops. All the inverted ‘Q’s will be high and the LEDs will be off. Since the inverted output from the last stage is connected to the ‘D’ input of the first stage, the first clock pulse from the astable flip-flop will set the ‘Q’ output high, and the inverted ‘Q’ will go low, turning on LED-4. Since the ‘D’ input of the next stage is now high, the next clock pulse will light LED-5, and the next clock will light LED-6, and the next LED-7. (Because we want a clean logic level to feed back to the ‘D’ input of the first stage, LED-7 is connected between ground and the true ‘Q’ output instead of Vcc and the inverted ‘Q’ output. This frees the inverted ‘Q’ output to drive only the input to the first stage.) On the fifth clock pulse, the first ‘D’ input will now be low, and LED-4 will be turned off. The next three clocks will sequentially turn off all the LEDs, and the cycle will repeat. |
|
| - Parts Placement and Assembly | |
|
The practice board can be kept whole, divided up into 8 individual PC boards, or any preferred combination. (More information and suggestions can be found in the “Assembly Options” section.) The parts are obviously very small, and should only be removed from their carriers and placed/installed on the PC board one at a time to keep them from getting mixed up or lost. This is especially true for the LEDs: they are not marked. The only way to identify them is by their color coded packaging or by running a current through them and seeing what color light they produce.
Note: Do Not Remove the carrier strips from their cards; just peal back the protective clear top strip to access one part at a time. It is recommended that the first section assembled be one of the ten component flip-flops. Start by placing the resistors. (These are the most robust components, and provide some level of protection for the semiconductors from static electric damage if they are placed first.) Though they have no preferred positioning, it is a good construction practice to orient them so that all their labels read in the same direction. This makes testing and trouble shooting easier- you will not have to keep spinning the board around to read component values.
For one of the Flip-Flop sections, with the board’s text right-side up, the ground connection should be toward the top edge and Vcc toward the bottom. The band on the capacitors should then be toward the Vcc, bottom edge of the PC board.
This is reversed for the Ring Counter sections- the band should be toward the top Vcc edge of the board:
Next install the two transistors. There is only one way they can easily be placed on their pads. Finally, special care must be taken when installing the two LEDs. First, they have polarity like the capacitors, and second, they must not be allowed to absorb moisture. They have no top side identity markings to identify what color they are, so remove them from the parts card and install them one at a time, or at least one color at a time. (Being so small, a few letters and numbers would block a lot of light.) They do have an arrow on the back that points to ground, and two tiny green tick marks on the front next to the cathode/ground solder terminal.
With text on the board right-side up, and the ground connection toward the top, the arrow/green tick marks should be pointing toward the top edge of the board. Note that surface
Once all components have been installed, check your work- are the right components in the right places? Have the capacitors and LEDs been placed so that they have the correct polarities? Are there any solder bridges that need to be removed? Most likely, if you were paying attention, and this is the first section you are assembling, everything will be in the right places. It will be that fifth or sixth module you assemble where false confidence can bite you. I know first hand. It is a learning process: “Good judgment comes from experience . . . And experience comes from bad judgment.”
Use clip leads or solder power connections to the Ground and Vcc (+ terminal) of the board. The board is designed to run on a supply voltage of from 2.5 to 5.5 volts, though its ideal voltage is 4.5 volts. (Three AA cells work very well.) Apply power to the board through a small resistor- around 47 ohms works well. This value is small enough that it will interfere with the circuits only slightly, but will help prevent a large flow of current from destroying the circuit if something is wrong. If all has gone well, the LEDs will blink away happily until power is removed. The 47 ohm resistor can now be removed. (If all has not gone well, refer to the trouble shooting section.) Now go and build the next section . . . |
|
| - Assembly Options | |
|
Though the kit’s circuits have been simplified to reduce cost and minimize errors, some small compromises were made to make the final display more interesting. Several different values for the timing resistors and capacitors are provided: 4.7uf and 10uf for the capacitors, and 47k, 75k and 100k for the resistors. These can be combined to provide the following timing values: Cap Resistor Approx. Delay time With a little care, the different colored LEDs can be placed where the user wishes. The only rule to follow is that the green LEDs must use a 150 ohm ballast resistor, while all the others use 510 ohms. (Due to their higher operating voltage and lower efficiency, the green LEDs need more current to match the light output of the other LEDs.) And to provide a little more color interest, 2 blue and two orange LEDs were added. The board can be assembled whole, section by section, or cut apart. The perforations in the board are there only to guide the divisions: |
|
| - Basic Trouble Shooting | |
|
Though the kit’s circuits are very simple, there are still many simple mistake that can be made that could prevent them from working. There is no simple straight forward set of “mistakes” to look for, though we hope to compile the most common ones from customer feedback. This is a short list of possible problems to look for. The main tool required will be a good digital volt meter. One with a built-in diode tester would be ideal. (If you are using a meter with an included thermocouple temperature sensor, it probably has this feature.) Possible problems & tests for the Astable flip-flop circuits: Test the individual components on the board without power applied. This should show up any bad solder joints, shorts, or damaged components. To check for open/cold solder joints, test the components solder joints by placing the test probes on the terminals of the component they are connected to. For example, to test LED-6 (D6) in the ring counter circuit, put the meter in ‘Diode Test’ mode and touch the red(+) probe tip to the Vcc power pad, and the black(-) probe tip to the neighboring terminals of R17. The diode’s voltage drop will show on the meter. (The LED will probably light faintly too.) If it reads ‘high’ or ‘open’, switch the test points. If the meter shows the diode’s voltage drop, it was installed backwards. If nothing changed, the diode is either not fully soldered, of was damaged during soldering. To rule out a damaged diode, touch the red(+) probe tip to the top terminal of D6, and the black(-) probe tip to its bottom terminal. If the diode’s voltage drop shows on the meter, then it is a bad solder joint.
As another example, use the ohm meter function to check the solder joints of test R15 by probing from D4’s bottom terminal to pin 2 of U1’s terminal. If it reads open, there is a bad solder joint. (Unless you can see gross, physical damage, it is unlikely that the resistor was damaged by soldering.) Transistors can be tested by using the diode function and probing from the emitter to the base, and the collector to the base. It should read like two diodes with their cathodes tied together at the base terminal for a PNP transistor. |
|
|
|
||||||||||
|
Taking Ideas into Reality | |||||||||
Edison was very insightful in his definition of genius. There are lots of good ideas and inspirations, but all by themselves they have little value. It takes effort and insight, tools, materials, and lots of time to bring them into solid existence. Applied Inspirations, LLC was founded to assist in bringing new ideas into physical reality by providing:
|
