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CONTACT MICROPHONE AND PREAMP
Piezoelectric transducer is a device that convert vibration energy in voltage or viceversa. Certains materials as ceramics or crystals have the ability of accumulate electric charge when are subjected to mechanical stress.
The circuit preamp amplifies a small signal to 3.2 times gain.
COMPONENTS
Veroboard
2 x 2.2 M resistors
100k resistor 220k resistor
100nF capacitor
3 x 10uF electrolytic capacitor
TL071 IC
IC socket
10k linear potentiometer
Jack connector
Minijack connector
Battery snap
SPDT Switch
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Shielded cable
Piezoelectric transducer
Minijack connector (male)
STEPS
1.­ Strip the shielded cable and pre­solder the shield on one side and the little cable from inside on another. For presolder take the stranded cable and roll, after put the iron soldering on the tip of rolled cable and pass the solder tin over the surface till cable is shiny silver
Solder the shield cable to the external and metallic part of the disk, then solder the hot wire to the white part. There can be no contact between wires or between the two areas of the disk. Put over solder joint a bit of hot glue for fix the cable to the disk preventing problems of use. Wrap all the transducer on pvc tape and submerge it on plasti dip can.
Once is dry, solder the other end of the cable to the minijack male connector.
2.­Cut the Veroboard with the measure that requires the project, in this case 11 x 8 holes, passing a cutting tool several times on each side of the board. Notice that it is necessary to cut in the next row of holes after the last row of your piece of board.
(The number of rows in the image on the left probably doesn’t match with the requirements of this project)
3.­ The Veroboard or Stripboard is a perforated board made of bakelite that in one side has strips of copper. The top side is where the components are placed. The bottom side is where the copper traces are, and where we gonna make the solder joints.
Now, we need to cut the traces of copper according to the plan of the project on page 1. As the view of the plan is from top side, to make the trace cuts we need to mirror the image. Here is a Piezo Preamp vero layout of the mirrored trace cuts:
The best way to cut the copper lines is to make the marked holes large enough to interrupt. Be sure that there is no copper connection remaining after you make the cut.
4.­ Time of Soldering! Begin with shorter components. Usually best option is to begin with the jumpers because sometimes another component needs to be placed over them. For the jumpers use a piece of wire. It doesn’t need to be isolated, don’t hesitate to unwrap the plastic cover if it is more comfortable for you.
For soldering properly you need to hold the iron in one hand and the solder tin in the other, fixing the iron tip on junction and approaching the solder tin depending on your needs. A good solder joint is shiny, without wrinkles or bulges and should cover all the hole of the board.
If your solder joint doesn’t look like it should, just give more heat with the iron until the tin expands over the copper trace.
At the time of IC sockets be sure that the mark is on the right position like it shows in the plan. Make sure too that the polarity of the electrolytic capacitor is in the correct way.
5.­ This step is called offboard wiring. Present the board into the container that you want to use as a enclosure. Think about the distribution of the space, the place for battery and the rest of components. Drill the holes on the enclosure and screw the minijack female connector, the jack female connector and the SPDT switch. Solder the red cable of the battery snap on the center pin of the SPDT switch. And one of the external pins to the spot called 9v (red) on the vero layout from page 1. Leave the last pin without connection. Solder the minijack connector tip pin to the input spot and the sleeve pin (ground) to the sleeve pin of the jack connector. Solder another cable from the sleeve pin of the jack connector to one of the GND spot of the board. Another cable from the tip pin of jack connector to the output spot on board. Solder the black cable of the battery snap to the second GND spot of the board. TACHAN! Try if works, if not, aghhht debugging!!! Be sure that everything is on the right place, polarity and values too. If it still doesn’t work, there is probably a shortcut: examine if there are solder joints that are connected to another lane or if there are undesired contacts between components. Examine if the trace cuts are perfect. Refill or reflow any solder joint that doesn’t cover the hole properly or does not look good. COMPLEMENTARY INFO
Humhack 2015