Sorry guys,

Theres always a new problem.
This time i bought 2 photodiodes. The black ones with 2 pins.
Well even when i expose the breadboard to complete darkness the led wont go off. I tried with 2 different photodiodes.
So whats the matter

 

Is it a photodiode or transistor? Your diagram shows a transistor. Part number?

 

It looks more like an infra-red LED than a photo-sensitive diode? Why would a light sensor be black (unless intended to detect only IR)?
Also, you seem to have the diode forward-biased (the wire with the 'flat' is connected to the resistor), so it will conduct in the light and in the dark.

 

Hello,

@Alec_t , the part can be a photo tansistor.
The SFH300 comes in blank and black:



Bertus

 

My diagram shows a transistor that is triggered by IR light. Hopefully this is normally what i bought. this stuff has no base. The base is the detector itself. At least this is what i learnt so far. My receipt says bpv10n - f=940nm

 

Hello,

The BPV10NF is a photo diode.
It can not be used the way you showed.

Have a look at chapter 21 of book three from this series:
https://archive.org/details/EncyclopediaOfElectronicComponents.Volume2CharlesPlatt

Bertus

 

That was my point. Try reversing it. The cathode is on the flat edge and it needs to be reverse biased.

 

That was my point. Try reversing it. The cathode is on the flat edge and it needs to be reverse biased.

Long lead on positive. Nothing happens when reversed

 

hi Yuseph,
Have you checked the Photo Diode data to show how much current will flow when illuminated , compared to the required current to light the LED.?
E

 

Long lead on positive. Nothing happens when reversed

That's what you want. No light, no current. It's only active with near infrared light (870 nm to 950 nm).* Get an IR source. An old fluorescent lamp may work. Better yet, get an IR LED. Maybe an IR backup lamp, night vision light, etc. will be available to you. It may also work outdoors. Near IR was discovered in sunlight.

*The datasheet describes the filter, which is why it appears so dark.

 

Supply voltage = 7.70v

Forward bias (long lead on positive)
Exposed to sunlight
Led =2v
Resistor = 4.85v
Photodiode = 0.74v

Forward bias
In the dark
Same values

Reverse bias
Exposed to sunlight
Led = 1.31v
Resistor = 0v
Photodiode = 6.40v

Reverse bias
In the dark
Led = 5mv
Resistor = 0v
Photodiode = 6.46v

No light at all when photodiode in reverse

 

A photodiode will conduct only a small current in the light - not enough to light an LED.
If you want it to work like that you could try something like an ORP12 - they get down to pretty low resistance in bright light.

 

Right. So that thing is useless.
I just want the component needed in my exercice book. The black led.
Ill see if i can find an orp12. But can you refer me to other references which are commonplace.
The book says phototransistor not photodiode btw

 

Hello,

You could amplify the signal of the photo diode with a transistor.
From the given book in the link:



Bertus

 

Here are some simple circuits you can try:


Source: https://ez.analog.com/design-tools-...todiode-wizard---cn-0312-spectroscopy-example

 

Hello,

You could amplify the signal of the photo diode with a transistor.
From the given book in the link:

View attachment 209338

Bertus

Excellent suggestion bro
The led glow but its so weak its ridiculous.
And it goes off when i cover the photodiode with something. So that works but the result is pathetic.
is there any practical use for a shit like that ?

 

hi Yuseph,
That fast Infra Red PD , is often used as a 904nm detector in pulsed Laser equipment, it must be amplified in order to drive another visible LED type.
E

 

Yuseph;

Your problem is similar to attempting a microphone to drive directly a speaker. It can't do it by itself, it won't unless you add an amplifier between the two.

That doesn't make the microphone pathetic or useless.

 

is there any practical use for a shit like that ?

The device apparently works as designed. Why did you buy it?

 

LDRs are a bit easier to work with for something like that. Here is a typical ckt.
The idea is when light the LDR is low resistance shorting to ground and not supplying enough current for the base of the transistor to turn on. At night the LDR is high and transitor turns on the LEDs. 100kΩ Pot to adjust sensitivity. Safety diode optional. 22kΩ on xstr base.