Belfry Frequency Division Detector

Schematic Diagram


eagle sch file*.

*Eagle is a layout editor from CADSoft, a freeware version is available (Win & Lin)

Parts List

component        description/value
SG1             transducer
SPK1            speaker
IC1, IC2, IC3   LM386 audio amplifier
IC4             CD4024 bit counter
C1              10 uF
C2              .047 uF
C3, C4          470 uF

Velleman / MA40A5R Ultrasound Receiver

RadioShack Cat.#: 900-6064 ($4.95)

A small 40 Khz ultrasound receiver. The bandwith of these piezo-transducers has a narrow peak around 40 khz. A group of students at UNN has measured it.

transducer photo

CD4024 bit counter

"The CD4024BC is a 7-stage ripple-carry binary counter. Buffered outputs are externally available from stages 1 through 7. The counter is reset to its logical "0" stage by a logical "1" on the reset input. The counter is advanced one count on the negative transition of each clock pulse."

A clock pulse for us one period of the amplified ultrasound signal.
Pin 6 (Q4) outputs the value (count / 16) % 2.
Pin 9 (Q3) outputs the value (count / 8) % 2. A value of 1 is a TTL logic true, 2 to 5 Volts.

Power dissipation: 700 mW
Operating voltage: 3 to 15 V
Fairchild CD4024.
datasheet (pdf)


LM386 audio amplifier

"The LM386 is a power amplifier designed for use in low voltage consumer applications. The gain is internally set to 20 to keep external part count low, but the addition of an external resistor and capacitor between pins 1 and 8 will increase the gain to any value up to 200."

National LM386
datasheet (pdf)


74HC393 dual bit counter

"The VHC393 is an advanced high speed CMOS 4-bit Binary Counter fabricated with silicon gate CMOS technology. It achieves the high speed operation similar to equivalent Bipolar Schottky TTL while maintaining the CMOS low power dissipation. It contains two independent counter circuits in one package, so that counting or frequency division of 8 binary bits can be achieved with one IC. This device changes state on the negative going transition of the CLOCK# pulse. The counter can be reset to "0" (Q0-Q3 = "L") by a HIGH at the CLEAR input regardless of other inputs."

This IC can be used as a low power alternative to the CD4024 (Bipolar TTL). Here pin 6 (QD) outputs the value (count / 16) % 2. The second bit counter on the IC is not used but should have its inputs grounded (pins 13 and 12).

Power dissipation: 4 uA at 5.5 V, or 22 uW (microwatt)
Operating voltage: 2 to 5.5 V

A 1 k resistor should be inserted between the 9 V power and pin 14 to ensure that only about 5 V, reaches the chip.
Fairchild 74VHC793.
datasheet (pdf)



RadioShack Cat.#: 910-3096 ($2.10)

"This 30mm diameter, 8-ohm speaker transducer is ideal for use in clocks, electronic toys, and miniature radios. It features a maximum power output of 0.2W with a frequency range of 500Hz - 12kHz and only weights 10 grams."

transducer photo
Last updated Sun Sep 10 17:53:40 EDT 2000