Electronic Circuits for the Hobbyist

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Circuits for the Hobbyist
For your electronics hobby entertainment; ENJOY!
It is assumed that you have AT LEAST the equivalent of a Basic Electronics certificate for the
electronics projects listed on this page. Other projects require more advanced electronics. A lot of
these circuits assume the latter so I will no longer answer the tons of emails in regards to that. If you
wish to learn more about electronics there is enough of that available on the internet.

Circuits' Message Board Ask your questions here. Someone may answer them.
ScanMate Your (Radio) scanner
Alternating On-Off Control
Audio Pre-Amplifier #1
Simplest R/C Circuit
Automatic 9-Volt Nicad Battery Charger
Simplest RF Transmitter
Basic IC MonoStable Multivibrator
Simple Transistor Audio PreAmplifier
Basic RF Oscillator #1
Single IC Audio Preamplifier
Basic LM3909 Led Flasher
Solar Cell NiCad Charger
Battery Monitor for 12V Lead-Acid
Battery Tester for 1.5 & 9V
Solid State Relay
Bench Top Powersupply, 0-30V/0-10A, Part 1
Third Brake Light Pulser
Bench Top Powersupply, 0-30V/0-10A, Part 2
Toroids, RF/EMI Cores
Bench Top Powersupply, 0-30V/0-10A, Part 3
Touch Activated Alarm System
Birdie Doorbell Ringer
Two-Tone Trainhorn
'Bug' Detector with Beep
Universal Flasher Circuit
Car Converter for 12V to 9V
Variable Power Supply, 1 - 30V @ 1.5A
Car NiCad Charger
Wailing Alarm
DC Motor Reversing Circuit
Water-level Sensing and Control
DC Motor Control Circuit
Waterpump Safety Guard for Fish-pond
Gel Cell Charger, I - Off-line
Weller WLC100 Electronic Soldering
Gel Cell Charger, II
Clock Generator
Christmas Lights Tester
Xmas Lights Tester
Continuity Tester, Low-Voltage
Zap Adapter
Continuity Tester, Smart
1.5V Tracking Transmitter
4-Transistor Tracking Transmitter
Continuity Tester, Latching

Cut Phone Line Detector
9-V Stabilized Powersupply
Dark/Light Activated Relay
30-Meter QRP Transmitter for Morse Code
Electronic Dazer
555 Timer IC Tester
Fluid-Level Detector
555 Go No/Go Tester More advanced
High Voltage circuits Interesting HV devices
741-Light Sensor
Lantern Flasher/Dimmer
Led Flasher, 2 transistor
Leds Flasher, alternately
LED Pilot Light (AC or DC)
555 Timer/Oscillator
Light Sensor With Hysteresis
741 Op-Amp
Logic Probe with pulse
Logic Probe with pulse, CMOS
Electronic Template
Micro-Spy with FETs
MosFet Test
Micro-Spy with USW
Piezo Education/Tutorial
Micro-Spy with TTL
PLL - Almost done!
Miniature FM Transmitter #1
Resistor Color Code Tutorial
Miniature FM Transmitter #2
SCR Tester
Miniature FM Transmitter #3
Triac Test
Mini-Drill variable Powersupply
UJT Test
Missing Pulse Detector (Basic)
Integrated Circuits
Morse Code Practice Keyer, I
Make Your Own Shunts
Morse Code Practice Keyer, II
Relays, Relay Drivers, Solid-State
Motor Accu Lader (Dutch)
Motorcycle Battery Charger
No-Hassle Third Brake Light
"Green" means on-line, "Red" means off-
9 to 9 pin (Female) Nullmodem Cable
Practical Intercom
Pulse Width modulator

8- Bookmark this valuable page with
RF Transmitter, light sensing
RJ45 Cable Tester
Radio Shack Special

Circuits Archive - Older circuits. Most are working, some are not. Could be still useful.
Radio Shack Partnumbers - Most common order numbers for my circuits
Tandy Corporation - European/Australian counterpart of Radio Shack
TUP/TUN/DUS/DUG European transistor replacement system
Tomi Engdahls' Page - Solid electronics projects!
Jan Freak's Page in the Netherlands - Well thought out information. Dutch language only
Bowden's Hobby Circuits - Collection of circuits, for everyone.
Circuit Exchange International - Andy's website. Good selection of excellent circuits
Electronic Tutorials - Collection of electronics tutorials.
Dolbowent.Com - Electronic Surplus and Engineering Support.
Jordan's Electronics Page - Lots of good circuits here also.
LED Webpage. White Led's everywhere - Malcom's site in the UK.
Guelph Amateur Radio Club - GARC--Official Homepage
PA3BWK's Ultimate Morse Code Website - Wilko Hollemans site in the Netherlands
Larry's Robotics & Electronics Page - Many good circuits
ElectronicsZone - Naveen's Website
Spark Museum - John D. Jenkins amazing collection of antique wireless & scientific instruments

DISCLAIMER: I take no responsibility whatsoever for the use and/or implementation thereof, or the
misuse leading to damage to equipment, property, or life, caused by the above circuits. Check with local,
provincial and federal laws before operating some of these devices. You may also check your life
insurance and/or the fact if they cover death by electrocution if you intend to play with Micro-wave
ovens and other lethal HV devices. Safety is a primary concern when working with high power circuits
or con/inverters. Play it safe!
to home page
Copyright © 1995 - Tony van Roon. ALL RIGHTS RESERVED.
Last Updated: August 7, 2002

Alternating ON-OFF Control
by Tony van Roon
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
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Copyright © Tony van Roon

Audio Pre-Amplifier
Additional Notes
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Published & Translated with permission of Jan Hamer, The Netherlands.
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 NTE834
Although 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.

If you have improved upon or know ways to improve it, Jan Hamer will appreciate your feedback. Klick on his name at the top of this page or contact him via his
website specified below. Thanks!
Please visit Jan Hamer's website in the Netherlands!
Return to Circuits Page
Copyright © 1995 - 2001 Tony van Roon

Basic IC MonoStable Multivibrator
by Tony van Roon
Back to Circuits page

Back to Circuits page

Document Outline

  • www.uoguelph.ca
    • Electronic Circuits for the Hobbyist
    • Alternating ON-OFF Control
    • Audio Pre-Amplifier
    • http://www.uoguelph.ca/~antoon/circ/nicd.htm
    • Basic IC MonoStable Multivibrator
    • Basic RF Oscillator
    • Basic LM3909 Led Flasher
    • http://www.uoguelph.ca/~antoon/circ/batmon12.htm
    • Battery Tester for 1.5 & 9V
    • Birdie Doorbell Ringer
    • Bug Detector with Beep
    • Car Converter, 12v to 9v
    • Battery Charger for Gelled Lead Acid
    • Clock Generator
    • Chrismas Lights Tester, xmas lights, kerstboom lichtjes
    • Continuity Tester
    • Smart Continuity Tester
    • Continuity, Latching Continuity Tester, Audio, Visual
    • ScanMate, your Radio Scanner scanner buddy!
    • Simplest R/C Circuit
    • Simplest RF Transmitter
    • Simple Transistor Audio Preamp
    • Single IC Audio Preamplifier
    • Solid State Relais
    • Pulsing Third Brake Light
    • Toroids, RF-Cores
    • Touch Activated Alarm System
    • Regulated Power Supply, Variable
    • Wailing Alarm Siren
    • Water-Level Sensor
    • Waterpump Safety Guard for Fish-pond
    • Repairing a Weller WLC100 Electronic Soldering Station
    • 1.5 Volt Tracking Transmitter
    • 4-Transistor Tracking Transmitter
    • Cut Phone Line Detector
    • Dark/Light Activated Relay
    • Electronic Dazer, High Voltage, Stun-Gun, Jacobs Ladder, Voltage Doubler, Ball of light
    • Fluid-Level Sensor
    • Lantern Dimmer/Flasher
    • Two Transistor LED Flasher
    • Two Transistor LED's Flasher
    • Led Pilot Light
    • Light Sensor with Hysteresis
    • Logic Probe with Pulse
    • CMOS Logic Probe
    • Micro-Spy with FETS
    • Micro-Spy 2
    • Micro-Spy 3, TTL
    • Miniature FM Transmitter #1
    • Miniature FM Transmitter #2
    • Miniature FM Transmitter #3
    • Mini-drill, pcb minidrill, print boormachine, adjustable powersupply
    • Stun Gun, Electronic Dazer, High Voltage
    • Morse Code Practice Oscillator
    • Morse Code Keyer (2)
    • Motorcycle Battery Charger, 12V
    • Third Brake Light
    • 9 to 9 Pin Nullmodem Cable
    • http://www.uoguelph.ca/~antoon/circ/intercom.html
    • Pulse Width Modulator, with the MC14093 Schmitt Trigger NAND
    • Light Sensing RF Transmitter
    • RJ45 Cable Tester
    • Mini-drill, pcb minidrill, print boormachine, adjustable powersupply
    • 30-Meter QRP (CW)
    • 555 Timer IC Tester, 555 Timer Tutorial with examples
    • 555 Timer Go-No/Go tester. 555, 741, PLL, capacitors, resistors, Tutorials with examples
    • 741 Op-Amp Sensor
    • Electronic Component Template
    • Circuit Archive, Archived Circuits
    • TUP, TUN, DUS, DUG