Birdle Doorbell Ringer

NotesP1 is of experimental value. Start with 220 Ohms or so and modify to suit your needs. The transistor is a general purpose kind and is not critical, almost any pnp type will work. L1 is a bell-transformer which is usually already present in the house. If you wish, you could use a battery instead of the bell transformer.

Just hookup a 9-volt battery to points 'A' and 'B' (A=+) the diode (D1) is to protect the circuit from accidental polarity reversal and is optional, but required for use with the bell transformer.T1 is a General Purpose PNP transistor and probably anything will work. L2 comes out of an old am transistor radio. They look like miniature transformers and are usually colored red or green. You have to fiddle with different transformers as the sound can vary depending on the value. The loudspeaker is a 8 Ohm type and must be larger than 200milli-Watt.

I used a 2Watt type, but anything over 0.2W will do. It really sounds like a bird and when you release the doorbell button the sound slowly fades away. I have used this circuit in my house for over 20 years and even build the "Birdie" for others. Although an old circuit, the experimentation and the final results still give a punch. Remember to Have fun!

By. Tony Van Roon

Battery Tester for 1.5 and 9V

Parts List:
R1 = 18K
R2 = 240 Ohm
R3 = 8.2K
R4 = 3K
R5 = 10 Ohm
M1 = Panel Meter (Anyone will work)

Design Considerations:
You may have experiment with the values of R3 and R4 to get an accurate reading from the meter. Every meter is different, so a little bit of playing with the resistor values is required.Try using a variable resistor in place of R3 & R4 to get a value of resistance that works.

By. Matthew B.

Battery Monitor for 12 Volt Lead-Acid

This simple circuit makes it posible to monitor the charging process to a higher level.Final adjustsments are simple and the only thing needed is a digital voltmeter for the necessary accuracy.Connect an input voltage of 12.65 volt between the positive and negative poles and adjust the 10K trimmer potentiometer until Led 10 lights up. Lower the voltage and in sequence all other Led's will light up. Check that Led 1 lights up at approximately 11.89 volts.At 12.65 volt and higher the battery is fully charged, and at 11.89 is considered 'empty'.The green Led's indicate that the battery capacity is more than 50%, the yellow Led's indicate a capacity of 30% - 50% and the red Led's less that 30%.

This circuit, with the components shown, uses less than 10mA. Ofcourse you can adapt this circuit to your own needs by making small modifications. The circuits above is set for 'DOT' mode, meaning only one Led at a time will be lit. If you wish to use the 'BAR' mode, then connect pin 9 to ground, but obviously with increased current consumption.The LED brightness can be adjusted up- or down by choosing a different value for the 4K7 resistor connected at pin 6/7You can also change the to monitoring voltage level. For example, let's say you wanted to change to 10 - 13 volt, you connect 13volt to the input (+ and -) and adjust the 10K potentiometer until Led 10 lights up. Change temporarily the resistors at pin 4 with a 200 Kilo-ohm potentiometer and reconnect a voltage from 10 Volt to the input. Now, re-adjust the 200K potentiometer until Led 1 lights up. When you are satisfied with the adjustment, feel free to exchange the 200K potentiometer with resistors again.(after measuring the resistance from the pot, obviously).

The diode 1N4007 was included to protect the circuit from a wrong polarity connection.It is however strongly recommended to connect the monitor directly to the battery, in principle a connection to the cigarrette lighter would suffice but for reasons unknown at this time the voltage at that point is 0.2 volt lower than the voltage measured directly on the battery. Could be some residual resistance caused by ignition switch and path through the fuse?

By. Jan Hamer

Basic RF Oscillator

This basic circuit is easy to build and the components are not critical. Most of them can be found in your junk parts box. The L1 antenna coil can be made by close winding 8 to 19 turns of 22 gauge insulated hookup wire around a ¼ inch fro such as a pencil. You can experiment with the size of the coil and the number ofof turns to see how it effects the frequency and signal output of the oscillator. You should be able to pick up its signal with a standard FM radio receiver. The “Signal” should be coupled by disc capasitor of about 0.1µF to the stage in front of it.

By. “antoon

Automatic 9 Volt Nicad Battery Charger

Good care given to your NiCad batteries will ensure a long life. However, they do need to be handled and charged with special care.It is therefore important to first discharge the NiCad to 1 Volt per cell, ensure that the battery is discharged, and then start the charge cycle.
Manufacturers recommend a charge current of 1/10th the capacity for a duration of about 15 hours uninterrupted.In reality, we learn some hard lessons when we forget to switch the charger off after the 15 hours and find that one or more cells inside the battery no longer accept a charge. That is the very reason that the circuit above is fully automated.The only thing to do is connect the battery and press the 'Start' button. When the discharge cycle is finished the circuit switches over to charge for 15 hours. After the 15 hours the circuits maintains a trickle charge to keep the battery 'topped-up'.Before I go into the schematic details I like to explain some of the component descriptions in the schematic. Jan Hamer lives in the Netherlands and so the circuit details are based on european standards.120E, 150E, etc. The 'E' just stands for Ohms so 120 ohm, 150 ohm. The original circuit specified the HEF type of cmos IC's which are not readily available in most of Canada. So just get any other type of CMOS chip like the MC4011, MC4020, MC4047 from Motorola. Any other type will do fine too. The BC548B is replaceble by a NTE123AP (NOTE: make sure it is the 'AP' type, the regular NTE123A is a total different transistor), ECG123AP, and the 2N3904 will work also. Watch for the correct pin locations since the BCE may be reversed with this european type. The LM317T is a TO-220 type and replaceble with a ECG956 or NTE956. The LM339N can be replaced with a ECG834 or NTE834Although this circuit looks quite impressive and maybe a bit difficult it is certainly not difficult to understand. The circuit needs to be hooked-up to a DC supply voltage of between 16.5 and max 17.5 volt, otherwise the CMOS IC's will go defective. Because I didn't feel like to design a seperate powersupply for this circuit I connected it to my fully adjustable bench top powersupply.First we connect a 'to-be-charged' 9-volt nicad battery to the appropriate connections. Then hook it up to the powersupply. Upon connection the 1nF capacitor starts up the two RS Flip-Flops formed by IC1a, IC1b, IC1c, IC1d, and pulls pins 3 and 10 'high' and pins 4 and 11 'low'. The clock pulses are created by the free-running multivibrator IC4. IC4's frequency is determined by the 10uF capacitors, the 220K resistor and the 100K trimpot. The clock runs continuesly but the counter behind, IC5, is not counting yet because pin 11 (the master-reset) is kept high. When the 'START' button is pressed, output pin 4 from IC1a goes high and biases TR4, which is made visible by the Red LED (D9) which remains lit. The NiCad is now being discharged via this transistor and the 100 ohm resistor.The 10K trimpot (at the right of the diagram) is adjusted in such a way that when the battery voltage dips below 7 volt, the output of IC3 goes LOW and the output pin 11 of IC1a HIGH. At hte same time the output pin 10 of IC1d goes LOW, and the red LED turns off.Because output pin 11 went HIGH the green LED (D8) lights up and at the same time the voltage level rises causing the battery to be charged. The charge-current is determined by the 120 ohm, 150 ohm, and the trimpot of 1K, at the right side of IC2. Actually we could have used one resistor, but the output voltage of different brands for IC2 may differ, by about 1.25 volt.Because the charging current is devided by value of the resistors, with the trimpot the current can be adjusted to the correct value of your own 9-volt NiCad. (In my case, the battery is a 140 mA type, so the charge current should be adjusted for 14 mA (c/0.1).At the same time the LOW of output pin 10 from IC1d starts the counter of the clock. On pin 9 of IC5 appear pulses which light up the red LED. This is implemented for two reasons, the clock-frequency can, with the 100K trimpot, be adjusted to the correct value; the red LED has to come ON for 6.59 seconds and for the same duration going OFF and except for that fact the green LED, who indicates the charge current, can be checked if the total charge-time is correct.When the counter has reached 8192 pulses ( x 6.59 = 53985.28 sec = 14.99 hours) the output pin 3 of IC5 goes high again, transistor Tr1 activates and resets the two flip-flops to the start position.The charging process stops and goes over to trickle charge via the 10K resistor and the D2 diode and keeps the battery topped-up.The adjustments of the project are really very simple and nothing to worry about. Turn the walker of the 10K pot in the direction of the 12K resistor, ground connection point of 10K resistor/diode D2, like the adjustment pin of IC2, apply a voltage of 7-volt to the battery connection terminals, switch the power ON and slowly turn the pot backward until the greeen LED starts to light up. Switch OFF the power and take away the connections you made to make the adjustment.Insert an amp-meter between the battery and the output connection and again switch the power ON. The battery will, in case it is not completely empty, totally discharged (to a safe level) and as soon as the 7 volt margin is reached goes over to the charge cycle. The charge current is at this time adjusted via the 1K trimpot (which is connected in series with the 150 Ohm resistor and in parallel with the 120 ohm resistor) accurately to the desired value.Addendum: It is strongly recommended to include small 100nF ceramic capacitors over the powersupply lines feeding EACH CMOS IC to keep possible interference to a negliable value.

Jan Hamer, The Netherlands.

Audio PreAmplifier

This easy circuit provides good gain to weak audio signal. Use it in front of an RF oscillator to make an RF transmitter that very sensitive to sound.


This preamp is very simple, and will work under tough conditions. The input impedance is pretty high, so it won't load down electric guitars. It will also amplify microphones. When I have a moment, I'll make some additions that will optimize it for microphones, and also show how to power a condenser microphone.

Source : Circuits for the Hobbyist

Alternating On-Off Control

Use this circuit instead of a standard on-off switch. Switching is very gentle. Connect unused input pins to an appropriate logic level. Unused output pins *MUST* be left open!. First 'push' switches ON, another 'push' switches OFF. You can use 1/4 watt resistors if they are metal-film type. Any proper substitute will work for Q1, including the european TUN's. For C2, if you find the relay acts not fast enough, leave it out or change to a ceramic cap between 10 and 100nF.
Parts List
All resistors are 1/2 Watt and 5% tolerance.
R1 = 10K
R2 = 100K
R3 = 10K
C1 = 0.1μF, Ceramic
C2 = 1μF/16V, Electrolytic
D1= 1N4001
Q1 = 2N4401 (ECG123AP, NTE123AP, etc.)
IC1 = 4069, CMOS, Hex Inverter (14069), or equivalent
S1 = Momentary on-switch

Source : Circuits for the Hobbyist
BY Tony van Roon