Bird Cry “my battery is low”

[markmi]

I build this little lipo battery monitor with a difference. Maybe some of the guys could use it in there onithopters.
The circuit consists of IC 4069 oscillating first at +-1sec and the second at +-2ms but before the second osc a large cap of 100µf is connected from the out pin of the low osc to delay the pulse so that it does not beep but squeak. C3 sets the high pitch and should be adjusted to mach the piezo buzzer to obtain a suitable sound. I have used a 100pf + 22pf placed on top of each other. Setting the voltage to activate the buzzer is done on R1 and R2 should be +-95k to 100k for a 2 Cell battery pack switching the voltage of 5.8-6V. Higher resistance is required for a 3 Cell battery pack. To calculate the resistance needed take a 100K linear pot with a 39k resistor soldered to the middle pin with a short piece of wire and the other pin just a piece of wire. Solder the two ends of wire to the PCB in the place where R1 and R2 fits, ground and the input of the TCM809. Turn the Pot up to max resistance and connect the PCB to an adjustable power supply, preset to 7V. Now turn the voltage down to the desired voltage + 0.1, let us use 6.1V for know. Adjust the pot connected to the PCB, slowly until the buzzer makes the squeaking sound, move the pot back and forwards so that you get the closest reading when the buzzer just cones on. Remove the pot from the PCB and measure its resistance. This will be the value for R1 and R2. Before soldering R1 and R2 hold them together and take there resistance, you might have to swap the with another one in the same value as they have a 5% tolerance leave. Here is the Schematics PCB layout with a sound sample.

[markmi]

Here is the 2nd circuit, I must say it should come with a warning hi audio levels and can cause hearing damage.
As described in circuit Bird Cry, setting the voltage leaves use the same mothered. The Piezo Element is very critical. I use a 12V alarm sounder. There is a small circuit board that has 1 Transistor, 1 Diode, 1 Inductor and 2 resistors. The whole unit size is dia.40mm and height of 35mm and gives a continues tone sound.
This circuit uses only the 3 terminal piezo element dia.35mm, smaller elements will not give the same audio level.
The output of this alarm is 35 to 40V at +-110 to 120dB at 20cm and in standby draws 20mA at 7V and 35mA at 6V when active. Pretty amassing for this circuit. The piezo element should not be removed from it housing as it requires pressure points to make it resonate.
The sound wave attached does not give this circuit just, as the speakers cannot deliver the same audio leave. So you will just have to build it.
This circuit can also be used for a HRADL device, Human Radar Airplane Down Locator. Remove the TCM809 IC and pull pin 1 low and turn around clockwise at 10 RPM and lysine for the sound. Big Ears has its advantages for this method. he-he

markmi