Replacing the 2N3904 with an SCR

So i made a laser alarm system some time back, it worked good but had one fault, more like a limitation. it made the buzzer ''buzz'' only when the laser was interrupted and the buzzer turned off when the laser was allowed to hit the photo sensor again. i wanted it to stay on until turned off by a switch. someone suggested something called a monostable flip flop but i had no idea what it even meant, then i saw something called silicon controlled rectifier or a thyristor, but i also learned that they have to be made using a pnp and npn transistor, what i cant understand is what transistors should i use to replace the npn transistor on my circuit, the tansistor on my cicuit is 2n3904, input voltage is 5v

Question by walee 1 year ago  |  last reply 1 year ago

SCR latching circuits and LEDs

LEDs and I just can get along...In another project I had a solenoid blowing out LEDs. Now this: I have a number of switches hooked up so they trigger an SCR latching circuit to turn on (and keep on) some LEDs. The SCRs are wired in parallel to each other and have a 1K resistor on the gate. Power is applied to the whole circuit via a timer relay (not hooked to the SCRs). The power is a 12v, 200mA wall wart. And the SCRs I'm using are NTE 5465. The LEDs last a while but burn out or go to a weird blinking state (when the switch is depressed) after about 2-3 days. In my previous project I needed a diode to help with the solenoid voltage spike. But I don't think that it is the case for this project since the SCRs aren't inductive. Do LEDs connected to the switch part of a relay need a diode too? The LED package I'm using is purchased from Happ Controls (see hideous grainy picture). It's rated for 12V but they can't give me a mA rating on them. But they say that no inline resistor is required. Any thoughts? I think this is another case of my inexperience causing me to overlook the obvious.

Topic by robotninjasquid 11 years ago  |  last reply 4 years ago

LED control via a reed switch and SCR

N00b question: I've got an RGB LED that has a forward voltage of 3.7v and a 3.7v battery pack. I want to trigger the LED to light via a magnet and reed switch. If I wire the reed switch to the gate of the SCR and have the SCR power the LED, will I be able to turn the LED on and off via the magnet by bringing the magnet near the reed switch?

Topic by d0ugparker 6 years ago  |  last reply 6 years ago

Where can i get a small SCR? Answered

 I checked the Radio shack website and haven't found any mention of SCR's.  I also found out that Radio shack is the only electronics store nearby.  I don't really want to have to order it in because my parents are really finicky about ordering things in and I was wondering if anyone knew of any common or cheap products that carry a small Silicon controlled rectifiers for me to salvage.

Question by DemonicRoss 9 years ago  |  last reply 9 years ago

Can anyone help me in designing a lignt chaser using SCR or triac?

I want to make a light chaser (240v bulb) using 555 4017 and SCR or TRIAC. Can any one help me doning this or have any reference schematic.

Question by Ankan Nayak 6 years ago  |  last reply 6 years ago

What can I scavenge high power triacs/scrs/ssrs from?

I'm doing some questionably safe experimentation and need some very high current method of pulsing AC in the 2-3KW range.  I also have no money and want things free off of craigslist, what appliances would likely have these parts in them?

Question by jasonuher 8 years ago  |  last reply 8 years ago

300 AMP SCR for sale

I have a 300 amp 1KV SCR I am saleing it for $25 shpping is $6 for in the USA

Topic by inductionheat! 8 years ago  |  last reply 5 years ago

What is the equivalent SCR of OE101?

Equivalent SCR with OE101 OR, Any SCR with 100V breakdown voltage and 1A forward current rating

Question by bishal 8 years ago  |  last reply 7 years ago

How to connect an scr to a coilgun?

I make the rwilsford07 boost converter and it charges my capacitor fine, but when I turn on the scr the 6v voltage regulator stop working(7806). What can be happening?

Question by Kurt Gerhard 7 years ago  |  last reply 7 years ago

2 free Fly back transformers and a SCR

I have one 300 AMP 1200 volt  SCR that I want gone!  I want $25 for it  . I am willing to trade it for crystal radio parts or small vacume tubes . I have two modern flybacks also if anyones interested sorry! dont have pictures

Topic by inductionheat! 8 years ago  |  last reply 2 years ago

I'm converting an old gas char-Broil outdoor grill,now used as a charcoal grill, to an electric smoker. See details.

For my initial design I'm using junk box parts (electronic hobbyist/pack rat).  The heating element is a 120vac, 500w burner previously used as an electric charcoal lighter.  The grill cavity is 15"H x 14"D x 25"W, with two rack heights leaving room for the burner, water pan, and possibly lava rocks/bricks.     The question is about temperature control.  I understand 500w may or may not be enough.  I'm considering a DIY full wave open loop SCR control, as I have many of the parts.  The purely resistive load is @2.4-2.5 amps and should be able to be temperature controlled using  demand oriented transfer or phase angle firing w/diacs.  I want maximum control cheaply and am having trouble selecting an appropriate design.  I have larger current SCR's in case I need a larger wattage elment. What can contributors suggest? 

Question by X-nfamous 3 years ago  |  last reply 3 years ago

How to use a SCR in a Coil Gun?

I want to increase the power of my capacitor but i can not figure out how to add a SCR. So i was wondering if somebody can show me how.

Question by Kante Tech 8 years ago  |  last reply 4 years ago

Can you put SCR's in parallel? Answered

The title said it all. The reason I want to do it is because I want to discharge a capacitor bank into a coilgun, etc, using SCR instead of a large switch. The surge current form the capacitor bank is approximately 400 amps and the SCR's I have can handle surge current of 160 amps, can I put a few of those in parallel to handle 400 amps?

Question by Plasmana 8 years ago  |  last reply 8 years ago

Where can SCR's be found in Australia?

I'm looking for some scr's (silicon controlled rectifiers) in australia but have so far been unable to locate any local suppliers. I'm using them *naturally* to switch the power for a multistage coilgun. So far i have been using high rated microswitches, but they are constantly failing and i've heard scr's provide the power quicker and more efficently.Thanks :)

Question by pyroten 9 years ago  |  last reply 9 years ago

How can I build a latching circuit without a Silicon Controlled Rectifier (SCR)?

I was wondering if there was a way to build a latching circuit without using an SCR because, after all, you can't get them at your neighborhood Shack, and I was wondering if you could use a couple of transistors or something similar.  Thanks in advance  -Julian

Question by jules15 9 years ago  |  last reply 9 years ago

What kind of SCR would I need for a coilgun with 2500uf 500vdc capacitors? Answered

Using a bank of 6 capacitors, all rated for 500 WVDC and 2500 uF. I'm only going to be mainly using them with 240 and 130 VDC. Would a 500Amp SCR be applicable?

Question by Mudbud 6 years ago  |  last reply 6 years ago

Is it possible to use an SCR to make a small solid state tesla coil? Answered

From what I understand, an SCR is like a diode that can either be turned on to act like an everyday diode, and it will only turn back off when the power is cut. With this understanding, will this circuit work? if not, can you explain? even if it doesn't work as a tesla coil, will it work as a fence charger (with a trigger transformer or ignition coil?)

Question by -max- 6 years ago  |  last reply 6 years ago

coilgun question, could someone explain what an SCR is to me and how to incorporate it in a coilgun circuit?

I am a novice "coilgun maker," and understand all the principals and such involved in it. now that im moving to more advance coilgun design, i need to understand what an SCR is/does. wiki can only teach u so much :D any help or answers to this question will b greatly appreciated!

Question by asantiago2 7 years ago  |  last reply 7 years ago

need new or used SCR for induction furnes!

Need new or used SCR for induction furnes! please any one who can help me! i need an SCR (Thyristor) , i dont care if its used or unused, i just cant justify the cost of a new one till i can be sure it will work; look at the picture below, iam replaceing the spark gap with an SCR. I put a drawing of a tesla coil diagram to compare with a simple spark gap induction drawing. $5 to $10 is in my price range till i know it will work. (voltage or amperage doesnt matter i would just like to see what there capable or if i can make it work for an induction furnes.)

Topic by Danielro10 10 years ago  |  last reply 10 years ago

Help needed with Wire Loop Game

Hello, I wish to make the Wire Loop Game for a childrens' fun-n-fair. But I wish to add a simple SCR/circuit so that the buzzer sounds continuously instead of momentarily, once the loop touches the other wire. Can someone please show me or direct me to a website with a simple SCR, which is easily available (in India since I'm from there) circuit that can do the job? Any help greatly appreciated! Thanks, Deboo

Topic by deboogeek 8 years ago

Help needed for making the WIre Loop Game Answered

Hello, I wish to make the Wire Loop Game for a childrens' fun-n-fair. But I wish to add a simple SCR/circuit so that the buzzer sounds continuously instead of momentarily, once the loop touches the other wire. Can someone please show me or direct me to a website with a simple SCR circuit, which is easily available (in India since I'm from there) that can do the job? If a readily available transistor can do this job, that would be good too. Any help greatly appreciated! Thanks, Deboo

Question by deboogeek 8 years ago  |  last reply 8 years ago

Many questions about multi-stage coilguns.

 May this be a big help for me and others who may stumble upon it. 1. I am controlling my coilgun with a PIC (PIC16F627A). What do I need to do in order to make it trigger SCRs? 2. What sort of external components do I need for the PIC (I'm sort of a newbie to electrical engineering)? 3. Regarding the actual coils, I am going to have 6 stages. How should the individual coils be made for maximum efficiency (I have heard that each successive stage should have less inductance, but I don't know exactly how this works)? 4. How does one go about slotting a metallic (brass) barrel while allowing optogates to work? 5. How exactly do you hook up the optogates to the microcontroller and to power sources? Any help on any of these questions would be greatly appreciated.

Question by moshee 9 years ago  |  last reply 7 years ago

Is a high ampere switch necessary?? Answered

I was going to try to build my now 2nd coil gun but this time wanted a solid state switch. after looking at the following: i was wondering if an 800A SCR is really necessary or can i just use a 16A SCR?

Question by MadScientist101 8 years ago  |  last reply 8 years ago

Easy/cheap way of halving the mains fequency in order to halve the speed of a single phase electric induction motor?

The problem is to slow the speed of an electric grinder down so that it does not burn woodturning HSS chisels during sharpening. I thought of full wave rectifying the mains and feeding it to a so-called "H-bridge" consisting of four SCR's. The SCR's on the top and bottom opposing sides are triggered together as pairs. Each pair of SCR's are triggered for two consecutive half cycles and so on. Might this work?

Question by hermanza 9 years ago  |  last reply 9 years ago

I have a question for people who have made/know coilguns.

Can anyone explain what an SCR does and where should i encorporate it in my coilgun design? Wiki can only teach you so much and i still can't quite grasp what it is/does.  also any other info for a rookie coilgun builder lol

Question by asantiago2 7 years ago

how to get water out of a DS and fix the blank screen on your ds ?

Question by lajefa100 6 years ago  |  last reply 6 years ago

circuit diagram and parts to repair 24 volt 20 amp battery charger uses Scr's?

I have a MAC 242011 battery charger  ( 24 volt 20 amp automatic battery charger I need a source and a cct diagram to repair . the Scrs are not working . can you help ? I am in Ottawa Canada tel cell leave txt message 613 291 9942

Question by PaulTieTenQuee 6 years ago

how to convert negative pulse to positive

Hello.. I built a transistor scr to turn on leds in my car from my remote.. my remote uses negative pulses to turn on and off... now the problem is that the scr needs a positive pulse to turn on but it uses negative to turn off,, so turning it off isn't a problem.. Im pretty sure I can just use a transistor to do this.. here is the schematic I used to build the scr...  ... fig 75b... is there a way to modify this circuit to make the turn-on negative or just a way to use another transistor to make my negative pulse positive? I could easily use an automotive relay to do this but im trying to make this as small as possible and its still on the breadboard.. I want to get this figured out before I put it on pcb.. thanks for your help

Topic by aclark32 5 years ago

Is there anything that can be done with an old screen from a laptop that has been "dissected"?

P.S. The screen is in good shape still, but the rest of the computer is pretty well dismantled.

Question by Mr. Thirty6 9 years ago  |  last reply 9 years ago

How do I make a rock tumbler? Perhaps not from scratch, but by adapting something else?

I'm not necessarily technically minded, so preferrably without having to rewire or solder things...

Question by juliemosaic 10 years ago  |  last reply 7 years ago

Questions about Capacitors Answered

Does the capacitance stack in a bank? Does the maximum allowed voltage? How do you wire an SCR? How do I determine what the total output voltage/amps will be?

Question by DELETED_Fuogger 7 years ago  |  last reply 7 years ago

Color Shift Dimming LEDs

Dim an incandescent, and it produces a mellow, warm orange sunset glow. Dim an LED, with the same SCR dimmer, and it flickers at 60 hertz, still producing harsh blueish light. How can LEDs more closely mimic incandescents?

Topic by Toga_Dan 3 years ago  |  last reply 3 years ago

convert negative pulse into positive using a transistor?

Hello... ive built an scr using transistors to turn on leds in my car with my remote.. my remote uses negative pulse.. now the scr(latching transistor) that ive built turns on with a positive pulse and off with negative.. so turning it off is not a problem.. I need to change the negative turn on pulse to positive to turn it on though. I know theres a simple way using a transistor to do this, but im still learning and my knowledge of transistors is still limited.. here is the schematic I used.. figure 75 b. I followed the schematic and it works just fine..  ... thanks for helping me out here

Question by aclark32 5 years ago  |  last reply 5 years ago

555 timer

I need help to understand how a 555 timer works, but mostly how I could build one. or if some ones willing to make one for me, i'll buy it, but it needs to have a ways to control it. well talk if your interested. I need it for a gate control for my SCR induction furnes.

Topic by Danielro10 10 years ago  |  last reply 7 years ago

How can i build a Scroll air compressor out of scraps and cheap material and power it from renewable energy ?

How can i build a Scroll air compressor out of scraps and cheap material and power it from renewable energy ?

Question by FeteLeToiMeme 8 years ago  |  last reply 8 years ago

would it be possible to bulk up gold flake for scrap ? Answered

Would it be possible to bulk up gold leaf/flake of a high purity with a resin/hardener to scrap ? as the jeweller will take a filing to test  would the bulking agent be minimal to detect  because it not being an alloy/metal ? love a bit of knowledge about this before i buy 30 kg of gold flake/leaf ;-P thanks   MAGIXO

Question by magixo 7 years ago  |  last reply 7 years ago

Capacitor charging circuit using bd243c. Will it work?? Answered

I recently made a schematic to charge a capacitor bank for my coilgun.D1-D4 are all 1n0007 t1 is a centre tapped transformer which will step up 12v to 330V. WIll it work. r1 and r2 are 10w resistors. Q1 and Q2 are BD243C with a rating of 65 watts.  i found my transformer from a very old cassette player. huge and heavy able to pump about 100W. i don't bother about charging time. I just want to know if it would be good. don't worry about the voltage monitoring i have a small voltmeter(like a watch. chinese product.) i am just want to know if it will work or not UPDATE: I have tried the shematic. It works flawlessly.  

Question by ARJOON 8 years ago  |  last reply 8 years ago

how to work this ac motor speed control circuit using 2AC input? Answered

Please let mo konw how to working this curcuit. I think Left one both ac input. So, SCR always turn on and off. than ac motor contineuly rotate isn' it?... But, this pic shows downscaling elevator moving circuit. I want some explain. plz someone help me.. left 15V both AC, right R1.T1 are 220V AC

Question by mr.kdy 4 years ago  |  last reply 4 years ago

How do I hook up a module camera directly to a screen.

I am trying to make a gadget that has a modular camera (something like this: directly to a modular screen (something like this: but I don’t want anything else on the screen. Is it possible directly or do I need a raspberry pi? If so how do I hook up the camera to the pi without the raspberry pi gui/clutter.

Question by EarthM 6 months ago  |  last reply 6 months ago

How to build a Gamecube Portable using the LCD screen and case from iBook G4 Apple Laptop? Answered

I would like to use an iBook G4 17" for the majority of the housing and screen for the portable. Heard I need an FPGA converter board to switch from VGA on the gamecube side to LVDS on the laptop side. I would like advice on how to best do that and also what kind of power supply I could use to run this system internally. External would be ok but internal even better! I have a gamecube and the iBook G4 already. 

Question by TriforceJunkie 6 years ago  |  last reply 6 years ago

Is it possible to use a 220v to 6v transformer for converting 6v to 220v DC to charge 250v capacitors?

Is it possible to use a 220v to 6v transformer for converting 6v to 220v DC to charge 250v capacitors? If yes, then can anyone give me a schematic for the circuit to = convert 6v DC to 220v DC, charge 250v capacitors ( @220v ), capacitor overcharge protection with something like resistor, capacitor full charging LED indicator, capacitor full charge LED indicator, SCR (Silicon-controlled rectifier) based capacitor discharge (use power for magnetic coil) circuit.

Question by manpatpro 6 years ago  |  last reply 6 years ago

Lighthouse pulsing light

Hi all - I am building a wooden model lighthouse, it will stand 5 feet tall and become my driveway landmark. I have been searching for a good light circuit, a non-LED version, preferably using 120v AC. I would like the light to just do a slow flash or pulse and haven't found a circuit anywhere. I did find one SCR simple circuit using a high rated capacitor, but I am looking for more options. I have a coloured halogen which should do the job well enough. So have any of you brainiacs come across any circuits close to this description - thank you for reading / responding. Bill

Topic by bstacy37 2 years ago  |  last reply 2 years ago

How do I build my own solar pathway light from scratch?

Hi There, I have just recently joined the site. I would love to make some sun jars as gifts. However most of the solar path lights are quite expensive here in South Africa and I might just as well just buy a sun jar rather than do it DIY ... Is there anyone who could point me to an instructable that shows you how to build the solar unit yourself (in short I want to build it from scratch) ... please bear in mind that I have two left thumbs, so the instructions would have to be quite clear. Thanks in advance to anyone who would be able to assist.

Question by Wilmich 9 years ago  |  last reply 7 years ago

Product recognition?

Hey, I have a science fair coming up and had a really good thought, however I'm not sure how I would go about doing it... So the thought is a refrigerator with product recognition abilities. Basically there will be something with basic information under a product (bottles, cans, etc.) which maybe has the expiration date and the bar-code number (maybe just the bar-code number). So in the fridge, there will be a sensor of some kind to recognize the products. Then that will be transferred to a computer so it can display a list of the things inside the refrigerator. I have a good knowledge of and basic knowledge of electronics (resistors, capacitors, transistors, SCRs etc.). I really have no idea for how this would work out, I know it's doable but not sure how.

Question by Seifpic 7 years ago  |  last reply 7 years ago


I've been under a great deal of stress lately. First off, there's the new school schedule. It cut lunch in half (By the time you get out of line with your food, lunch is over), doubled the amount of homework, and cut the time you have to do that work in half. (It basically scr*wed everyone) This schedule was supposedly based on a school vote (I guarantee at least 90% of the student body voted NO), but those "votes" went strait to the shredder. I've been doing 5-6 hours of homework every night. To add to this stress, I had my driving test, which I thankfully passed. That isn't the worst of it though. A few days ago we found a bloody lump on Mazee's neck, and we are worried sick that it is cancer. She went into surgery yesterday to get it removed, and we are anxiously waiting for the test results. Mazee has been crying and moaning all day, and I feel really bad about it. IT'S NOT CANCER! :DIt was Benign Hemangioma, a non-cancerous tumor.

Topic by Spl1nt3rC3ll 10 years ago  |  last reply 10 years ago

Variable DC input to a clean AC out put

So here is what I am trying to accomplish. I am trying to take an old Jacobs wind turbine controller that was designed for a grid tie application and make it off grid. There is a 3 phase "wild" ac input from the turbine that is rectifyed but not clipped by the internal SCR's to variable DC (40-180 volts). The sensing was designed to tie to the grid and power sync'd to line power and freq then exported or imported depending on demand. What I would like to do is build a Variable Dc input inverter that will put out a pure sine wave 120/240 vac split phase. Thus imprinting a usable power out put and allowing the cap/choke inverter to do its part. The design need not handle much power as it is only used as an imprint to regulate the power through the controller. If anyone had any idea on a build for this or a manufacturer that is producing such an item I could really use some ideas. Thanks

Topic by nbrooks 8 years ago

Electrolytic vs supercap for CD spotwelder?

I need to make a cheap spotwelder to rebuild some battery packs(e.g,. welding thin nickel strips).My options are:(a) Try to find most of a farad at up to 25V or so on eBay. This could take a while. (Buying new electrolytics in the 0.1F range and above at these voltages is pretty expensive.)(b) Go for supercaps from Digikey (e.g). They've got some 5V 1F models for only a few bucks, and some "fast-discharge" ones for 10x more. Of course, if I go for more than 10V or so, I'll have to build some sort of charge-balancing circuit around the series caps, and I'd rather not unless it's really the best way to go--- though it might be as simple as a resistor in parallel to each cap.(c) Try one of these weirdo "digital supercapacitors" that are all over eBay for the crowd who fill their entire trunk with stereo amps. These look like they're rated at 1-5F at 13.8V and (I would hope) include some sort of charge balancer. Dunno if they're suitable for the sort of instant-discharge I want for a welder, though.I'm having difficulty figuring out:(a) How fast a discharge I need for a spotwelder anyway; I'm going to be using an SCR to trigger it and presumably want the lowest-inductance arrangement I can get, but are we talking milliseconds or microseconds?(b) What can I get out of a supercap? Milliseconds or microseconds? I haven't worked with supercaps before, and most people who seem to be designing circuits with them are using them as batteries.Other random questions:My reference design had 0.5 to 1F at 0-25V through a 600V 50A TO-65 SCR; whatworries me are things like,whose page 3 shows that non-ultra-low-ESR supercaps (e.g., theaffordable ones) seem to have virtually no capacitance for pulsewidths of 10ms or less. (The BestCaps in that datasheet claimsomething like 60% of nominal instead, which is pretty good!)I dunno how narrow the pulse width needs to be to get good welds,but I'm guessing pretty narrow---for example, one guy claimed in that just the difference inputting the SCR on the low side and not the high side (so the triggerfor it didn't have to go through the wires, electrodes, and workpiece)worked a whole lot better, which implies to me that he might betalking microseconds. But I just don't know.]Of course, I also don't know whether I need 0.5 F at 10V or 1F at25V for the things I'm considering.Not to mention---the 50F caps at of which claim ESR's of 0.025 ohm at 1kHz) have these skinny little0.5mm leads on them. How in hell would these leads not be vaporized if Icharged up the cap and then shorted it, as a spot-welder would be doing?(And sure, I could try to attach #4 copper wire to them---somehow---andsend that to the sharpened tips on my welding electrodes, but boy I feelsilly doing that---seems like whatever part of the cap's leads aren'tattached to the heavy wire will just evaporate when shorted, if they canreally dump that kind of current, even if it -is- just for milli-to-microseconds.)The Instructables site has some rambling about using supercaps for CDspotwelders, but it's just rambling---nobody who's actually built oneusing them, for example, or who seems to talk about discharge rates,etc.

Topic by HilaryGage 11 years ago  |  last reply 11 years ago

Do i need to use this output from my DC motor speed control board?

Hi With the goal of using the DC treadmill style motor that i have in a project (or two), i have baught a SCR speed control board. The circuitry of the control board has outputs for the armature and field coil (labeled "excitation"). But the motor that i have is a permanent magnet type (2 wires going in / out  - red and black - nice and simple). So i don't need the 'excitation' output. My question is whether the control board needs this to be used? Am i going to fry my brand new controller if i only draw current through the armature output? I could, for instance, put a resistive load accross this output to make it use just less than the output it's rated for. Here's more info on the parts in question: The speed controller is like this:;=item3a9488e567 or this:;=item4adc7e0294 The motor is either of the models on this page (i actually have one of each): Thanks in advance. Peas

Question by balisticsquirel 4 years ago  |  last reply 4 years ago