Nuts and Volts - June 2010

■ Vibration Monitor Schematic.

battery compartment’s spring.

I had trouble making a contact for the other end of the board. At first, I tried to make a contact similar to the positive end of a battery but the contact was poor and intermittent. I ended up taking a 3/4” length of solder braid and soldering it to the bottom square pad on the board with its tail coming out to the right side. When putting the board into the box, I threaded it through the contact slot and into the first turn of the spring for the battery (on the left). This solved the problem.

If you want to have adjustable sensitivity, solder the R2 alternate potentiometer to the board and leave the fixed R2 vacant. Mount the two ICs, diodes, and R1 and R2 (if you want fixed amplification) to the top of the board. The square pads are pin 1. Watch the polarity of C1 and bend the leads so C1 will lie flat on the board and then solder. Screw a 3/8” 2-56 screw from the top side into the tapped hole.

Turn the board over. Bend the piezo transducer leads at right angles where the contacts enlarge (no polarity) and solder on the bottom side of the board. Make sure that the sensor is centered with the board and that the piezo film is about 1/16” above the bottom (of the board) so that it can vibrate. Solder the speaker, noting its polarity on the bottom side. The screw should be protruding next to the speaker.

Testing

Place the board into the center position of the battery compartment and add two AA batteries to each side (note their polarities). Turn on the switch and set the unit on a quiet counter. After a minute, strike the counter with your hand. This should sound the alarm. Reset the unit by turning off the switch.

Once the unit is tested, glue the speaker to the bottom of the box so the board will not move. Replace the battery cover and secure it with the small screw to the battery case.

Uses PARTS LIST ITEM QTY Battery Holder 1 ea C1 1 ea D1-D2 2 ea IC 1 1 ea IC 2 1 ea Piezo Vibration Detector 1 ea R1 1 ea R2 1 ea R2 Alternate 1 ea Screw 1 ea Speaker 1 ea Board Pre-programmed chip Shipping and handling

1 ea 1 ea

DESCRIPTION
12BH331/CS-GR
10 µF 16 volt radial
1N914
PIC12F508
MCP601
LDT0-0128K
100K 1/8 watt
1,000 1/8 watt
100K potentiometer
2-56 3/8”
WT-1205

SUPPLIER

Eagle-plastics.com Microchip.com Microchip.com Meas-Spec.com Soberton.com

$10.00*

$5.00*

*Ron Newton
2230 Damon Rd.
Carson City, NV 89701
sjnewt@att.net
775 885-8842

This device can be used as an intrusion alarm or as an earthquake detector by changing its amplification. How about as a computer alarm if you walk away from your desk? It also could be used for analyzing motor vibration frequencies, or perhaps as an anti-feedback controller for microphones since there is plenty of room for more code. For remote monitoring, a relay can be substituted in place of C1 and the speaker. Run wires to a light or bell.