How to add a bicolour LED to "ghost detector" circuit - Page 1
Forum section: electronics / beginners

author: yada
author_rank: Frequent Contributor
timestamp: May 11, 2017, 07:46:56 pm
content: Here is the circuit, all it does is a make an 8M gain off the base of the first transistor.So I want to change it where when the circuits off(not detecting) it displays one colour of an LED then when it detects it changes color in a bi coloured LED. Would be best if the first colour went out with the second turning on, that way it fades into it. The circuit is going into a little box and running off a 9V batt for kids to play with, so I don't want to mess with a micro or arduino. Just something simple in case they break it, lose it, or get board with it.I really have no idea as to where to start looking for how to do this or what the circuit would be called.

author: Buriedcode
author_rank: Super Contributor
timestamp: May 11, 2017, 08:18:34 pm
content: Generally, there are:"bicolour" LED's: Two LED dies wired back to back in the same mould, two leads. Requires reversing polarity to light, or more commonly, a 50% duty square wave on one lead, and hi/lo/high-Z on the other."tricolour" LED's: Two LED dies with commoned anodes or cathodes, three leads. Independent control/current for each LED.Generally, tricolors are easier to work with, but by using a 50% square wave on a bicolour, and varying the duty of PWM on the other lead you can effectively fade between the two colours for a bicolour as well.It sounds like you want it to switch between the colours - so one LED is always on, indicating power, or.. to fade between the two colours?

author: sanwal209
author_rank: Regular Contributor
timestamp: May 11, 2017, 08:19:11 pm
content: Hi. I have modified the schematic for you. This will work all you need to do is to replace two leds with bicolor led and choose the R3 and R4 according to the LED you will buy.Goodluck

author: yada
author_rank: Frequent Contributor
timestamp: May 11, 2017, 08:26:54 pm
content: Quote from: sanwal209 on May 11, 2017, 08:19:11 pmI should add its a tricolour LED with a common +. Now to look at the schematic THANKSEDIT: That should work with a common anode because each cathode goes to its own transistor?But why does that work? It seems like both LED would turn on at the same time or D2 being more sensitive so that after D2 turns to full bright D1 would tart turning on?

author: yada
author_rank: Frequent Contributor
timestamp: May 11, 2017, 08:53:43 pm
content: So both LED stay on all the time. Even with no wire hooked up to the base of T1 (left=T1 to right most= T4).Should I add to the 1M resist to 2M and take 100k to 200k? I'm going to play around with the values but when I do I like to know the theory behind it, rather then just try random values and hope it works by luck.Problem is that there is just too much gain right? its taking the stray current from INSIDE T1 or its lead and amplifying it?

author: Paul Price
author_rank: Super Contributor
timestamp: May 11, 2017, 09:20:25 pm
content: I wonder how many ghosts are viewing this topic?If you really want a really great ghost detector, aura detector, life-energy detector, acupuncture point detector..you are using the wrong parts!Instead use the input pins of a CD4030 Quad CMOS Exclusive OR Gate and the sense electrode areas will be so sensitive that they can can actually be inside the black box case.It will be so much more sensitive than your transistor designand allows connecting a red-yellow combo LED in several different ways to the gate outputs and as a bonus, much longer battery life.Hint; the reference ground point of the circuit should be a metallic or conductive area opposite the sensor areas. You have 4 gates to play with but two are all you need for a three-pin LED. Only one current limited resistor required for the LED. You can put a 1-meg series resistor to the inputs to limit electrostatic damage to the IC from rug-generated static HV sparks people can carry around. Ground unused input pins for max. battery life.

author: sanwal209
author_rank: Regular Contributor
timestamp: May 11, 2017, 09:42:05 pm
content: No they should not turn ON at the same time as i did simulation before sending it to you. Try giving input logic 5v and 0 then see either both turn ON or not. If yes then we will see later whats the problem.

author: mmagin
author_rank: Frequent Contributor
timestamp: May 11, 2017, 10:54:33 pm
content: I've seen a bipolar version of this exact circuit, lit up one of two leds based on polarity of the charge on a sense electrode. I think it was just this plus a complementary circuit made with PNP transistors.

author: yada
author_rank: Frequent Contributor
timestamp: May 11, 2017, 11:20:59 pm
content: Quote from: sanwal209 on May 11, 2017, 09:42:05 pmSo I do have a second ATX power supply that I made, as the one I'm currently using is a vellman that measures the mA (well worth the $230.00 American, plus its handheld and made in Austria, all the best stuff is made in Austria, my most expensive piece of lab equipment).Should I use +12 and +5 from the ATX and try it, or can I tie the vellman ground and ATX ground together, using the ATX for the five volts? I would hate to kill this vellman power supply, I don't know how I lived without it or how I would live with out it. Or could I tie a 9 volt battery to an external power supply with a common - ? Or are you saying the just attach the +5 with no ground and see if it senses the current?BTW I don't have any exclusive ORgate IC's to play with and no electronics stores in my area.

author: yada
author_rank: Frequent Contributor
timestamp: May 12, 2017, 01:29:13 am
content: So I removed R1 R2 and R5 making that completely open and both LED light. So current is flowing backwards from the circuits point of view? Powers going from emitter of T4 to the base of t3 then out to the LED which I guess is why it was always on, the first two transistors or any of them are not acting like amps they are just being diodes. Hmmm...

author: sanwal209
author_rank: Regular Contributor
timestamp: May 12, 2017, 07:29:45 am
content: Yes you can use power supply but add 1.2K resistor in series between the power supply and first Transistor. Install Proteus and i will send you design files and you can simulate it.

author: yada
author_rank: Frequent Contributor
timestamp: May 12, 2017, 07:32:27 am
content: Quote from: sanwal209 on May 12, 2017, 07:29:45 amProteus? Looking for that right now, this is a gift so I'm eager to get it working and in the post...Unless proteus is a sea god I cant find it... hmm...

author: Zero999
author_rank: Super Contributor
timestamp: May 12, 2017, 12:54:47 pm
content: Quote from: sanwal209 on May 11, 2017, 09:42:05 pmWhat's the current through D1 when Q3 is off? It will be around 2mA which will make D1 glow dimly. You need to add a resistor across it to drop the voltage below the turn on voltage.

author: yada
author_rank: Frequent Contributor
timestamp: May 12, 2017, 08:59:23 pm
content: So I re built this circuit and the LED just stays on, this thing is haunted. I used BC337 instead of 457. but It worked in the first version. What is the difference?

author: Zero999
author_rank: Super Contributor
timestamp: May 13, 2017, 10:42:41 pm
content: Quote from: yada on May 12, 2017, 08:59:23 pmTry connecting the base to 0V to check that it's still working and one of the transistors haven't failed closed circuit.

author: yada
author_rank: Frequent Contributor
timestamp: May 17, 2017, 07:35:17 am
content: Quote from: Hero999 on May 13, 2017, 10:42:41 pmThat must be what it is. I did measure the all the voltages and they were not what I expected, I will find where I wrote them down and we can try and figure it out. Each base needs to get 0.6 volts or it wont turn on correct? I think I remember the led being on and one base measuring 0.15 volts but the LED was on. The base at trans 2 was right at 0.6. I removed all the resistors and the LED still lit, like a series circuit through the trans. That's one thing I never expect: to build the same circuit twice and have it work differently. Are cheap multimeter trans tester worth anything, or just so they can write more marketing wank on the box?