• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Can opto-couplers be opened up to be light activated? (ie used for their phototransistor)

Triode

Active Member
Is there a reasonable way to open up an optocoupler to be light activated? Or is that a extremely delicate operation to attempt?

My son's snap circuits kit has a broken phototransistor. It uses it for several of the projects where light pulses make a tone from a speaker, or a fiber optic cable triggers a motor. It's fun stuff. But his phototransistor got broken off, and the leads snapped off inside so I can't seem to get a wire onto them. I don't have any phototransistors that work with visible light on me, it's just not a component I've had much occasion to use. But I have a ton of optocouplers with NPN phototransistors inside. If not I can put one in my next parts order, but this would get it working soon, and it's been a favorite activity of his while all the playgrounds are closed. Snap circuits have been sort of the science part of his home schooling lately.

Thanks!
 

Ramussons

Active Member
Basically you want a Photo Transistor. You will need to know whether it is a PNP or NPN. But why cannibalize an opto coupler? Why not buy a PT?
Can we have some photos of the Zone 0?
 

tomizett

Active Member
Depends on what facilities you've available... I would have though that if you held it firmly-but-gently in a vise and filed flat down from the top with a fine-ish file you might be able to expose the transistor. If you've a bench grinder available, hold it in a pair of pliers, against the toolrest, and try the same.
Got to be worth a go if you've got optos to spare.

Don't forget to post us some pictures! :)
 

atferrari

Well-Known Member
Get a low power transistor with the type of your preference with metallic encapsulation.

File the top carefully (that means, with patience) and you could get a useful PT. Clean the white goo inside, if any, and you are in business.

Did that with 2N2222, 2N3711 and even with a 2N3055.
 
Last edited:

gophert

Well-Known Member
Most Helpful Member
Get a low power transistor with the type if your preferente with metalic encapsulation.

File the top carefully (that means, with patience) and you could get a useful PT. Clean the white goo inside, if any, and you are in business.

Did that with 2N2222, 2N3711 and even with a 2N3055.
Clipping the seam with some micro-side cutters also works. The metal hat lifts right off.

My micro-side cutters were never the same but the students were really impressed with a DIY phototransistor.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Get a low power transistor with the type if your preferente with metalic encapsulation.

File the top carefully (that means, with patience) and you could get a useful PT. Clean the white goo inside, if any, and you are in business.

Did that with 2N2222, 2N3711 and even with a 2N3055.
You were many years too late :D

The classic example was the OC71 - which was a black painted glass encapsulated germanium transistor.

It was also available as a phototransistor, cunning called the OCP71, at a greatly inflated price.

Needless to say, it didn't take long until enterprising people found that simply scrapping the paint off an OC71 gave you an OCP71 for a fraction of the price.

As a result of this Mullard (the manufacturer) starting using opaque grease inside the standard OC71's.
 

gophert

Well-Known Member
Most Helpful Member
You were many years too late :D
Don't fool yourself, atferrari knowingly brought forward a vintage solution so I don't think it would be possible to be "many years too late". I think YOU just needed to feel smart today - another case of "Nigel-splaining".
 
Last edited:

MaxHeadRoom78

Well-Known Member
I remember that when I had a early transistor radio to fix, the owner's asked curiously why the volume went up when he opened the back of the radio,
A couple of OC71's used with the paint flaking off answered the question.! :p
Max.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
Get a low power transistor with the type of your preferente with metalic encapsulation.

File the top carefully (that means, with patience) and you could get a useful PT. Clean the white goo inside, if any, and you are in business.
Just tried it out of curiosity - a BC477 from my misc semiconductors box, RS branded.

It works, no "goo" to clean and a very obvious switch-on effect when exposed to moderately bright light (changing from no reading to 60K on my meter). It would probably need to feed the base of another transistor to function as a serious switch, but definitely a functional phototransistor.

BC477_opened.jpg
 

JimB

Super Moderator
Most Helpful Member
Don't fool yourself, @atferrari knowingly brought forward a vintage solution so I don't think it would be possible to be "many years too late". I think YOU just needed to feel smart today - another case of "Nigel-splaining".
I would say that it is more like a variation of a theme.
ATF suggested opening a metal can
NG suggested scraping the paint from a glass/plastic case.

And all this lead to another case of "gophert-splaining".


Ay up, thes' nowt as queer as folk, tha' noz.

JimB
 

atferrari

Well-Known Member
NN of unknown origin most likely, salvage.
From a test, probably pre-pandemic this year.20201016_184452.jpg
 

Triode

Active Member
well that didn't work, his kit uses visible light and these gates are all IR.

I do think I have some metal can NPN transistors around, and probably a few hundred in plastic cases. I'll give that a try.

And as for why I'm doing this, well I did order some but this is very educational and I think it's great how my son is into these electronic kits. He's7, if he has to wait a week he may lose interest.
 

gophert

Well-Known Member
Most Helpful Member
I would say that it is more like a variation of a theme.
ATF suggested opening a metal can
NG suggested scraping the paint from a glass/plastic case.

And all this lead to another case of "gophert-splaining".


Ay up, thes' nowt as queer as folk, tha' noz.

JimB
You proposed that clear plastic cans and metal cans both hold a photo active semiconductor but claim the concept is somehow completely different In each case. However, my point was, atferrari could not be late for proposing a vintage solution. Do you agree with Nigel that atferrari was "many years too late" with his suggestion as Nigel accused? Or did you completely misunderstand my post?
 
Last edited:

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
You can pop the case on a TO-3 package with a vise. Squeeze near the solid end. I remember doing the photo-transistor thing with a HeNe laser.
 

Triode

Active Member
You can pop the case on a TO-3 package with a vise. Squeeze near the solid end. I remember doing the photo-transistor thing with a HeNe laser.
I just gave that a try, there's a type that I have about 200 of that are NPN and the right current rating for his kit. It popped and exposed the die, but in this case it didn't work anymore. I probably cracked it. But with them being worth a few cents each I can afford to give it a few tries.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
Do you agree with Nigel that @atferrari was "many years too late" with his suggestion as Nigel accused?
I'd paraphrase it as "It's hardly a new idea".

(And sorry, but you seem to just be picky and argumentative for the sake of it. It's bit like people that jump on a typo or spelling mistake and ignore the main topic in an answer).
 

Nigel Goodwin

Super Moderator
Most Helpful Member
I'd paraphrase it as "It's hardly a new idea".

(And sorry, but you seem to just be picky and argumentative for the sake of it. It's bit like people that jump on a typo or spelling mistake and ignore the main topic in an answer).
It seems to be his only reason for been here?, perhaps he should get a life?.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Just tried it out of curiosity - a BC477 from my misc semiconductors box, RS branded.

It works, no "goo" to clean and a very obvious switch-on effect when exposed to moderately bright light (changing from no reading to 60K on my meter). It would probably need to feed the base of another transistor to function as a serious switch, but definitely a functional phototransistor.

View attachment 127526
May I just say I absolutely love the 'hinged' top :D
 

Latest threads

EE World Online Articles

Loading
Top