LDR circuit ( Application of transistor as switch)

[CDRIVE]

Here, but as you can see with a little field expedience and red neck engineering you can make your own test points.

http://www.ebay.com/itm/200-Keyston...158?pt=LH_DefaultDomain_0&hash=item2c64b3ae2e

 

[vick5821]

Yes..Okay

 

[CDRIVE]

Hey, do you think my that LDR project is a good project to develop a teaching aid for secondary schools in Malaysia? Thank you

Regarding this question sent via PM.. Earlier in this thread a member, I think it was CocaCola, mentioned that he prefers permanent analog meters for teaching aids. I totally agree with him or whoever posted that. In fact, as a teaching aid, I think this project should incorporate two meters. One measuring base current and the other measuring collector current. This way the student can clearly see the gain relationship between the two simultaneously.

As far as how to build this in a manner that's intended for the classroom is concerned.. When I was a young'n nearly everything I built was centered around a wooden board with point to point wiring. Come to think of it, PCB's didn't exist when I was very young. Some of the most beautiful antique electronics were done this way. Malaysia has Mahogany up the ying yang along with other beautiful woods. Take a peek at these links, especially this one.

http://peeblesoriginals.com/catalog/45.php

About midway down the page you'll see one of his projects with the components clearly drawn on the surface of the board. A design like this is perfect for the classroom. Here's some others.

http://images.search.yahoo.com/imag...dt&sigi=14h0pdqk4&sigb=11v44l4ja&fr=yfp-t-701

Keep in mind that back in their day ALL of our great inventors used this approach.

 

[vick5821]

Ammeter? Then must be a micro ammeter?

 

[CDRIVE]

Ammeter? Then must be a micro ammeter?

Ammeter is a generic term. It doesn't specify the range you're measuring. Besides a 0 to 50uA meter movement can be shunted to measure....

0 to 500uA
0 to 5mA
0 to 50ma
0 to 500mA
0 to 5A
0 to 50A
0 to 500A

Likewise, it can be multiplied to measure ...

0 to 500mV
0 to 5V
0 to 50V
0 to 500V
0 to 5KV

If the full scale has markings for 1 & 5 or 10 & 50 you can make even more ranges for both current and voltage.

 

[vick5821]

Ammeter is a generic term. It doesn't specify the range you're measuring. Besides a 0 to 50uA meter movement can be shunted to measure....

0 to 500uA
0 to 5mA
0 to 50ma
0 to 500mA
0 to 5A
0 to 50A
0 to 500A

Likewise, it can be multiplied to measure ...

0 to 500mV
0 to 5V
0 to 50V
0 to 500V
0 to 5KV

If the full scale has markings for 1 & 5 or 10 & 50 you can make even more ranges for both current and voltage.

Oh yea. agree to that. But it is the best to get the one that suitable for my this project which measure a very small current

 

[CocaCola]

When I was a young'n nearly everything I built was centered around a wooden board with point to point wiring.

I was going to actually suggest point to point wiring using a plastic cutting board... Doing one of these approaches you can 'oversize' everything and make connections and the circuit more clear... You can even get fancy and mock up a larger than life transistor that slides over the real thing for visual effect...

 

[CDRIVE]

<snip>... You can even get fancy and mock up a larger than life transistor that slides over the real thing for visual effect...

I think I love this idea. The visuals would be great.

 

[CocaCola]

I think I love this idea. The visuals would be great.

If you love that you would really love going overboard and mounting a LED grid/display or even an LCD display in the oversized transistor that simulates the real time effect happening inside

It's all a matter of how far someone wants to take it, I'm all for the visual effect in a teaching environment (I believe it really helps drive home what is happening) thus the more the better... But, of course you are limited by budget and practicality...

The oversized transistor is a easy mock up, you can whack on out of even a block of wood pretty quickly, drill out the bottom, wire some 'heavier' gauge wire to the real transistor for oversized leads on the oversized device and then pot the bottom to hold it all together... You could have a golf ball or base ball sized working transistor with little work... A lot more impressive for students to look at vs a black lentil bean with legs

 

[CDRIVE]

You could have a golf ball or base ball sized working transistor with little work... A lot more impressive for students to look at vs a black lentil bean with legs

I don't want to hijack this this thread but I must relate this memory. It was July in 1963. The place was S Company of the 2nd Training Regiment at Ft. Dix New Jersey. We were all gathered in the woods where an elevated deck was built for the DI's to be seen and heard easily. We were in our second week of chemical warfare training and the DI was discussing the symptoms of being exposed to nerve gas. After he got that out of the way he informed us that one of the items that a soldier would carry in his first aid kit was an Atropine antidote. With that he reached down and held this object over his head with two hands. It was about 3 feet long and looked like a gigantic tube of tooth paste with a one foot length of 1/2" dia pipe sticking out of one end. The end of the pipe was cut at an angle of a syringe. He told us that if we detect any of the symptoms we have only minutes to jam this thing deep into a leg muscle and squeeze the tube or we will be dead!

Someone should have had a camera to capture the expressions on our faces. You could hear mumblings everywhere saying "You gotta be kidding, I'd rather die"!

Yes, it was a training mock up but we didn't know that and the DI loved this part of the show. The real thing was less than 4" long, needle included.

 

[vick5821]

I was going to actually suggest point to point wiring using a plastic cutting board... Doing one of these approaches you can 'oversize' everything and make connections and the circuit more clear... You can even get fancy and mock up a larger than life transistor that slides over the real thing for visual effect...

Means not using stripboard, donut board or PCB ? But the way, how will I make that to become neat and much professional ?

 

[CocaCola]

If you use a plastic cutting board it's already non conductive, once you map out your circuit (use graph paper) you can transfer then it to the cutting board, mark any wire junction or 90° turn and drill a hole at those points so that you can install screws... Now with all the screws in place it's just a matter of stretching wire between and around screws...

 

[vick5821]

If you use a plastic cutting board it's already non conductive, once you map out your circuit (use graph paper) you can transfer then it to the cutting board, mark any wire junction or 90° turn and drill a hole at those points so that you can install screws... Now with all the screws in place it's just a matter of stretching wire between and around screws...

Oh. Make all the connection visible. So I think better to use something like transparent perspex ? It involves small components like transistor

 

[CocaCola]

Yes, for a teaching aid all the connections should be visible, or else you are not teaching No need for clear unless you want to sandwich the wires, just run them on the surface... As I said for the transistor I would mock up a larger than life one, and us that... Heck I would like to help make one of those larger than life ones for you but the darn International shipping would be stupid expensive vs you doing it yourself...

 

[vick5821]

Yes, for a teaching aid all the connections should be visible, or else you are not teaching No need for clear unless you want to sandwich the wires, just run them on the surface... As I said for the transistor I would mock up a larger than life one, and us that... Heck I would like to help make one of those larger than life ones for you but the darn International shipping would be stupid expensive vs you doing it yourself...

How to make a larger than life one ? Wow. Thank you for your intention

 

[vick5821]

Yes, for a teaching aid all the connections should be visible, or else you are not teaching No need for clear unless you want to sandwich the wires, just run them on the surface... As I said for the transistor I would mock up a larger than life one, and us that... Heck I would like to help make one of those larger than life ones for you but the darn International shipping would be stupid expensive vs you doing it yourself...

Actually, I am not sure if I get what you mean for that idea or not. Kinda blur @@

The wires are top of the board or bottom ? I only need to solder the wires to the component directly ?

 

[CocaCola]

How I would do it an how you would do it are probably different, that is why I suggested making one out of wood, as most people will be able to do that...

I have a full wood working shop as well as a metal lathe and milling machine at my disposal... I also have experience in casting liquid resins and modeling in CAD that can be rapid prototyped among other things... Expecting you to have the same and telling you how I would do it using those tools and skills probably isn't going to work out well...

There are lots of low cost options to do, if wood is out of the question, you could model it up in some oven bake clay like Fimo, bake it in the oven and you get a plastic like solid model... The bake temp of Fimo is just over 212°F (100°C) and I highly suspect that baking the real transistor inside your big model likely isn't going to damage it at all...

 

[CocaCola]

The wires are top of the board or bottom ? I only need to solder the wires to the component directly ?

On the top in clear view, use the screws for most connections and solder only if necessary... Think of it as a big stab lock prototype board, but instead of stab locks you are using screws...

 

[vick5821]

Do you have some pictures for a better imagination purpose ? You tried to make one too ?

 

[CocaCola]

Something like http://www.snapcircuits.net/ notice how everything is exaggerated and big and out in the open?