Wow these are small, Photo Light Sensitive Photoresistor

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gary350 said:
That is 40 years of dust and dirt setting on work bench or shelf. What is the best way to clean that up. I have trouble with bad connections contacts must be very dirty.
Click to expand...

They do wear out - spring tension sags and surfaces oxidize. Spring for a new set, 3 for $8 on Amazon.


Or cheaper on eBay...

**broken link removed**
 

That is cheaper than they use to be. I paid about $20 for mine at Radio Shack long time ago. What is the real name of these things? They use to be called breadboards. Names of many things have changed over the ages. I could probably clean mine up a little nicer with a tooth brush. I just bought 100 Red LEDs 99¢ free shipping.
 
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I worked in industry for 40 years American companies have their parts made in China. Engineering department puts specifications on the parts and quality control makes sure all parts from china meet factory specifications. This saves everyone lots of money not having to pay union workers $78 per hour. NO down time for union workers going on strike wanting higher pay. Unions were started by Al Kapone & Frank Nitti in the early 1900s to make them self richer. Complain all you want about china made parts they make parts for US to OUR specifications. China is the best thing that ever happened to this country too many greedy middle men getting rich at the expense of others.

I have not found any china parts that don't work. Resistors quality is 1000% better than 40 years ago I test new china resistors they are all extremely accurate within a few ohm. 40 years ago a 1,000,000. ohm resistor would be plus or minus 5% at best = plus or minus 50K ohms. I test new caps they are more accurate than 40 years ago too and they all work. ICs, mosfets, diodes, transistors, LEDs, they all work.
 
American and European companies have their products made in China but then do good engineering and do proper quality control.
Many Chinese companies pickup "sweepings off the floor" or discarded defective American or European parts. There are entire huge cities in China that make only fake electronic parts to be sold on ebay and Ali-whatever.
 
This is something I learned long ago with neon flashers. All 3 of these circuits use the same amount of power from the battery.

The 50uf cap produces a very tiny quick flash not very bright in the dark.

The 100uf cap produces a very good flash perfect after dark.

The 200uf cap produces a very bright flash I wonder if this can shorten the life of the LED ???????

Instead of using a 200uf cap to get a longer 2 sec flash rate higher resistance works better.

audioguru, yes I know that too. I am having good luck with cheap china parts. It probably would not be good to use them in hospital equipment or military equipment or anything that needs to be 100% dependable. Some of the factories I once worked in sold reject parts they did not care what the buyer was doing with them it was better money than the scrap metal yard.

 
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Our vision sees short durations as being dimmed which is why Pulse Width Modulation works for dimmers.
Your 50uF and 470 ohm LED flasher simply use the capacitor discharging with a current ramp into the LED. Its average light is not the peak current and it is a short duration so it is dim.
My LED flashers use a Schmitt trigger producing a rectangular pulse of 30ms which is long enough for our vision to see the actual brightness but the duration is short so the battery lasts for a long time. Increasing the on-time of my LED flashers does not increase the brightness but reducing the pulse width causes dimming.
 
I need to know more about Schmitt trigger I might be able to use that in this project.

This is my first prototype I hung it on a trellis before dark. As it slowly gets dark all 3 LEDs slowly come ON. When voltage gets high enough the flasher starts to blink. The unit did good all night running on 2 AAA batteries. This morning as it slowly became light RED LEDs stopped flashing and slowly got dimmer and dimmer until all 3 LEDs are off. The light detector circuit has a yellow LED that stays ON all night it uses unnecessary power from the battery, this LED needs to be OFF or removed to save battery power it defeats the purpose of the light detector circuit. The 2 Red LEDs blink rate is 2 seconds at a distance it appears to be 1 LED blink rate of 1 second.

What is the resistance of an LED? Yellow LED needs to be gone then maybe R3 = 340 ohms needs to be higher. Flasher should still work maybe better with larger voltage across a larger resistor. No sure how to prevent this unit from slowly coming ON & slowly going OFF ? Is it possible to put a voltage multiplier between Q1 & Q2 to increase 2.07v to 3v ?

Each time I come up with a new simple project I run into new problems all of them very educational for me. At my age I have a terrible time remembering new things I need to take better notes. I remember what I learned in college 50 yrs ago better than what I learned yesterday.

 
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The light detector can be a Schmitt Trigger circuit to suddenly switch the LED blinker on or off.
A 74HC00 IC has four Schmitt Trigger gate circuits in it and works from a supply that is 2V to 6V. It draws very little battery current but has enough output current to light LEDs.
One Schmitt Trigger can be the light detector and a second Schmitt Trigger can be an oscillator driving the 1st LED and a third Schmitt Trigger can be an inverter to drive the 2nd LED.
 

I put an alligator clip across LED 1 to short it out the light detector no longer works. I tried to ohm an LED I get no reading on any meter setting. I increased R3 to 470 ohms light detector works & flasher still works too. I looked at data sheet for 74HC00 I have no clue what this does? It says TTL login but it is not in my TTL book. I found information that says, 74HC00 see 7408 flip flop. TTL Book does not tell how 7408 works there must be a circuit that sets the speed? All I need is 1 flashing RED LED with a light detector that operates on 2 D batteries. There is no circuit information? I need information how 74HC00 works a circuit drawing and educational write up how to design a circuit. I can't fine youtube video how 74HC00 works.
 
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The 7400/ 74HC00 is not a schmitt trigger device.

Look at the CMOS 4093 or 40106; they both have schmitt trigger inputs.

You can use one input of a 4093 gate for the on/off control and another for for the flasher oscillator,then the other three sections in parallel as a buffer to drive the LED.
 

What is the defination of input? Voltage, switch, AC, DC, low resistance, high resistance, capacitor, ??????????

After checking out the data sheet is this correct?

LDR is 500 ohms to 1M ohm

 
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I was thinking about using the high output current of 74HCxxx ICs that can drive an LED but a 74HC132 is a Schmitt Trigger quad 2-inputs NAND gate.
The 2-inputs gate is needed so that both LEDs can be turned off when there is light on the photocell.

Since the 74HC132 has NAND gates then a gate can be a simple Schmitt Trigger inverter when one input is always set to be high.

The 74HC132 is Cmos so its inputs are controlled by voltage, the input current is extremely low.
 
I accidentally made an improvement on this circuit. I decided to replace R3 with a variable resistor to see if higher resistance will increase the 2.07 volts. I forgot to disconnect the battery soon as I unsoldered the resistor LEDs got brighter and started blinking slower closer to the correct flash rate. Higher voltage make flasher blink slower. Voltage is up to 2.4V with yellow LED & R3 gone. Is there a way to get 2.4v up closer to 3v ?

 
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You have 2.4V because Q1 is not saturated because its base current is too low. The base current is only (3.2V - 0.7V)/57k= 43.8uA.
If the red LEDs are 1.8V red ones then the 470 ohm resistors limit their current to try to be (3.2V - 0.2V - 0.2V - 1.8V)/470= 2.1mA but then the base current must be 0.21mA which is 210uA. Change R1 plus R2 to 15k but then the photo-resistor will need more light to turn off the circuit and R1 will draw more current during daytime.
 
I had to make 1 small change to the circuit. I walked out to the street 200 ft away 2 LEDs blinking look like 1 LED. I could cover 1 Red LED with tape but decided to replace 1 Red LED with a Yellow LED. Now it is very noticable 2 lights are blinking. 2.4V is making very bright flashing LEDs very easy to see. The 100uf caps are taking a good size charge making more than enough light. The LED Blinker circuit ran for 1 month with 2 AAA batteries and 4 months with 2 D batteries. I can let it run with 2 AAA to see if it will run 1 month with the Light Detector circuit that has been added. If the circuit runs 1 month like before nothing gained. If it runs more than 1 month the light detector is saving battery power not blinking all day in the sun too. LDR is very sensitive days will soon be shorter than they are now. If battery life is increased 50% then 2 D batteries will last 6 months instead of 4 months. It will take a month to learn how well the light detector circuit is working. Instead of waiting a whole month maybe I can use my amp meter to test it if it reads that low. Tomorrow is another day, I need to get 1 of the LED blinkers with no Light Detector working tomorrow and test both circuits on the amp meter. Here is the final circuit drawing.

There is no cardboard tube on LDR this circuit is plenty sensitive LEDs are trying to turn ON in the evening in a time span of 10 minutes. LEDs are trying to turn OFF in the morning in about 10 minutes.

 
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