Ding Dong Touch Bell
"Ding dong bell" is a popular nursery rhyme. Shake-speare used the phrase "ding dong bell" in several plays. Today, ding dong is a popular ringtone used in phones and door bells. Here is a simple ding dong tone generator circuit built around a dedicated analogue IC.
Circuit and working
Fig. 1 shows the circuit of ding dong tone generator. The circuit is built around BT8031 ding dong IC, CD4049 inverting buffer, op-amp 741, transistors BD678 and BC547, touch plate, speaker and a few discrete components. It requires 9V DC supply.
BT8031 is a 3-pin ding dong IC in TO-92 package with operating voltage of 1.3-3.3V.
As seen from the circuit, the touch signal from the touch plate is picked up by op-amp IC 741 (IC1), and inverted and buffered by IC CD4049 (IC2). Output pin 6 of IC2 drives BT8031 (IC3) through resistor R5. Zener diode ZD1 regulates the supply to 2.2V required by IC3. 2.2V is fed to Vcc pin of BT8031, which outputs ding dong signal at its MO pin. This output tone cannot drive the speaker (LS1) directly. Therefore BC547 and BD678 transistors are used as amplifier stages.
Working of the circuit is simple. A touch on the touch plate is detected and a ding dong sound produced by the speaker immediately.
Construction and testing
An actual-size, single-side PCB for the ding dong tone generator circuit is shown in Fig. 2 and its component layout in Fig. 3. Mount the components on the PCB. Use IC bases for IC1 and IC2. Solder the ding dong IC on the PCB. Pin details of BT8031 IC are shown in Fig. 4. The touch plate can be a piezoelectric plate taken out from a buzzer or it can be formed by two copper wires or two copper tracks fabricated on a PCB as shown in Fig. 5. Points A and B are connecting terminals to the circuit. Preset VR1 is used to control the sensitivity of the touch plate.
To test the circuit for proper functioning, touch the touch plate to produce ding dong sound. If there is no output from the speaker, check the voltage status at various test points as per the table.
If the circuit is working well, enclose it in a suitable cabinet. Use a 9V PP3 battery or any 9V DC adaptor for powering the circuit.
Circuit and working
Fig. 1 shows the circuit of ding dong tone generator. The circuit is built around BT8031 ding dong IC, CD4049 inverting buffer, op-amp 741, transistors BD678 and BC547, touch plate, speaker and a few discrete components. It requires 9V DC supply.
 Fig. 1: Circuit of ding dong tone generator |
As seen from the circuit, the touch signal from the touch plate is picked up by op-amp IC 741 (IC1), and inverted and buffered by IC CD4049 (IC2). Output pin 6 of IC2 drives BT8031 (IC3) through resistor R5. Zener diode ZD1 regulates the supply to 2.2V required by IC3. 2.2V is fed to Vcc pin of BT8031, which outputs ding dong signal at its MO pin. This output tone cannot drive the speaker (LS1) directly. Therefore BC547 and BD678 transistors are used as amplifier stages.
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 Fig. 2: An actual-size, single-side PCB for the ding dong tone generator |  Fig. 3: Component layout for the PCB |
Construction and testing
An actual-size, single-side PCB for the ding dong tone generator circuit is shown in Fig. 2 and its component layout in Fig. 3. Mount the components on the PCB. Use IC bases for IC1 and IC2. Solder the ding dong IC on the PCB. Pin details of BT8031 IC are shown in Fig. 4. The touch plate can be a piezoelectric plate taken out from a buzzer or it can be formed by two copper wires or two copper tracks fabricated on a PCB as shown in Fig. 5. Points A and B are connecting terminals to the circuit. Preset VR1 is used to control the sensitivity of the touch plate.
 Fig. 4: Pin details of BT8031 IC |
 Fig. 5: Suggested touch plate |  Fig. 6: Touch plate PCB |
If the circuit is working well, enclose it in a suitable cabinet. Use a 9V PP3 battery or any 9V DC adaptor for powering the circuit.
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