Sunday, May 08, 2016
Recently i captured this circuit in eagle to publish online, it seems to have a small design error. It worked well for many years. The step-down transformer is used as a step-up here. The secondary winding was around 50mA so the resistance was protecting the 2N2222. (SL100 was used in the original one). C1 and R3 may need tweaking to get the desired adjustment range in R2.
Circuits using only discrete devices
The voltage across the speaker is fed to C1-Gnd, which blocks DC component. R1, R2, R3 form a threshold bias for T1. 2N2222 chops the 12V DC in tune with the music. The chopped DC current flowing in the 12V winding of TR1 is stepped up into AC pulses over 100V, this lights the Neon in flashes synchronizing in real-time with the beats. Known Issues - It does not perform well at low Bass like 20Hz.
Thursday, March 05, 2015
RASON Projects Page - Amateur Radio
- 10 Amp, 13.8 Volt Power Supply
- 12 Volt Gel Cell Charger
- Thermal Fan Controller
- Transistor Audio Amplifiers
- 12 Volt Gel Cell Charger
- Switching Regulator Basics
Many modern HF transceivers come fully equipped with built in tuners. While these tuners are great for changing bands, the manufacturers left out a very important accessory; the 4 to 1 balun. With out a balun the transceiver can only feed an antenna which uses coaxial cable.
The Radio Amateur Society of Norwich
P.O. Box 329 - Norwich, Connecticut 06360
Sunday, October 26, 2014
Aaron Cake Electronics
The Schematic Symbol Reference, How To Solder and Desolder helped many electronic beginners in building their Projects. This was a valuable resource in those days even though it appears common today. The internet was used to genuinely share useful learning and ideas.
Wednesday, October 22, 2014
Schematics, Hobby Projects, Tesla, Marconi, 555, Metal Detecting, Electronics-Tutorials and a lot more..
Circuit Land - Tony Van Roon
- Morse Code Practice Keyer,
- Constant Current Charger
- Touch Activated Alarm System
- Miniature FM Transmitter
- Continuity Tester, Smart
Sunday, November 17, 2013
BD139 is used to drive the relay as it has good Ic. So you can even use a low ohm relay. If a Relay resistance is high its quality is higher, its power consumption is less and it needs thinner wire SWG-AWG. T2 and T3 form a darlington pair which drives T1. LED1 shows that the water level has reached the top of tank and also that the Relay is energised. D1 a freewheeling diode. R3 10M ensures that the high gain input does not float, yet the low leakage current thru the water is not drawn away by the 10M. R2 limits base current in case water is saline.
See more at Circuits with Discrete devices
Friday, March 23, 2012
This supply gives both positive and negative outputs. Appropriate Fuses should be used to protect from fire hazard and overload of transformer.
The Filter capacitor C1 4700uF has an impedance of Xc = 1 / (2 * 3.14 * f * C) which comes to 0.6 ohms at 50 Hz. The impedance of the load at 2A for 24V is R = V / I that is 12 Ohms which is more than 20 times the impedance of the capacitor at 50 Hz. That means less than 1 / 20 of ripple current will flow thru the load. The Regulator also reduces the ripple a little.
Monday, February 20, 2012
There are many better circuits in the various circuit archives i have linked on the front page, you just have to look around. When you measure the open circuit voltage of a battery with a high impedance DMM (10M), the value may be a bit misleading. Apply a dummy load to bleed the battery a bit so that proper readings can be taken on Load. The load below is a 100 ohms wire-wound fusible ceramic resistor which will heat a bit when you test 12V batteries.
Theory of Operation.R16 a 5W ceramic wire wound bleeder or dummy load. R15 is a part of an attenuator for obtaining ranges. D2 is a protection clamp diode. R10-D1 forms the 5V reference for comparators. Then an attenuator obtains 1.2, 1.4, 1.6, 1.8 V steps for each comparator. This circuit is similar to Audio Level meter or VU meter circuit.
The comparator compares the battery sample voltage to the fixed reference step. If '+' pin is more positive than '-', or is '+' is more dominant, then output goes floating 'open collector', so No LED light . But if '-' is more dominant the output transistor of comparator goes low impedance or saturates or turns 'ON'. But only spec current can be switched, do not compare with electrical switch 'ON'. Also on a dual supply 0V is more dominant or positive compared with -12V, even though it appears -12V is a big number. The direction of current is what decides, all measurements are relative.
Saturday, December 18, 2010
Constant Current Source LED Drive
This is a Constant Current Source LED Driver, When the LED driver Upper-NPN is driven by a voltage thru 4.7K the LED lights up. Assume that the Lower-NPN at bottom is absent. The current via LED and NPN is limited by R. 20mA may be ok 15mA even better. Or LED blows even transistor goes.
BC547 is like 100mA-40V-200b, Limit collector current to 60mA, use it at less than 25V and depending on the individual transistor you may get a DC current amplification of 200 times. That is 1uA of base-emitter current could give a whooping 200uA of collector-emitter current.
Still Thinking we do not have the Lower-NPN we calculate the resistor. Vcc - ( 2 LEDs * 1.7) - Vce = Vr that is the voltage across the resistor. You know ohms law and the current needs to be 15mA for a bright and long lasting LED. Lastly 1.7 the forward drop of a green LED and 0.6 a saturated or Turrned-On NPN Vce.
Now you use the Lower-NPN, The above calculations do not hold anymore. Let us think a small current is flowing in the LED. Then the voltage across R is less than 0.7V, that means base-emitter diode of the Lower-NPN will not get to conduct. The Collector does not draw any current away. Now think that more current flows in LED, the voltage across R builds up above 0.7V the Lower-NPN is biased. The collector of Lower-NPN starts drinking current from the base of the Upper-NPN. So The Upper-NPN starts losing its bias. This lowers the LED current and contains, regulates or controls the LED current as shown in the formula.
BC847/BC547 series; 45 V, 100 mA NPN general-purpose transistors
LEDMUSEUM.ORG-THE LED MUSEUM-Reviews of LEDs
FET Current Source
This is a constant current source using a FET. This is the most simple replacement to series resistor to limit current. The N-Channel FET BF256C can give 15mA current.
- A current source based on a JFET
- 4QD-TEC: Current sources and mirrors
- Current source - Wikipedia, the free encyclopedia
- Field effect transistor - Wikipedia, the free encyclopedia
More at - Schematics of delabs: LED-Circuits
Friday, December 17, 2010
These circuits were drawn for a person in Africa. See the thread here… stabilizer circuit. They were not tested by me, but are quite close to a practical design.
This circuit is a design i did, not tested by me as yet. It can Stabilize Mains voltage to around +/- 10% . It can be used for both 110V AC or 220V AC inputs with modifications. The Output is 220V AC. There is an overload, under voltage and over voltage trip circuit. With some tweaks and modifications it might work.
This circuit is a design concept, not tested by me and i did it just to explain some ideas. The circuit uses opto-coupler MOC3041 of Motorola and the Triac BTA-16-600 of ST as a solid state switch or relay. It also uses the LM324 quad opamp from National Semiconductor which is low power and single supply. As the MOC3041 switches the Triac at zero crossover there is no inter-winding short of transformer on crossover hopefully, the control circuit is designed in such a way that more than one triac will not be turned on at a time, i would like you to give feedback.