What? Dimming LEDs? I thought we were working on a piano keyboard.
The ramp circuit is a response to what Martinez was searching for...ramps. See? It even has a piano key on the left side.

Anyway, a ramp is part of a pwm, and a ramp can end in a down ramp or a sudden stop. This being a piano, I expected a sudden stop unless one of the pedals is depressed.

Yeah... I forgot to explain that in more detail.. my bad..

What chillum wants is to build this circuit, which produces funny sounds when the light changes:



And wants to replace the optotransistors with opto-couplers, and he wants to ramp-up the leds inside optocouplers to produce the sounds he wants. That's why he needs to build a ramp up circuit first. Here's the source page.

 

does it have to be 2N4416

You are so getting ahead of yourself right now! The 4416 is merely my favorite jfet. It isn't right for this job. Look at how Martinez had to use a 100 uf capacitor to slow the ramp down.

 

You are so getting ahead of yourself right now! The 4416 is merely my favorite jfet. It isn't right for this job. Look at how Martinez had to use a 100 uf capacitor to slow the ramp down.

But is the ramp up circuit the right approach to replace the optotransistors? Or should we go back to PWM?

 

I finally got Mantech to quit showing me mosfets and jfet input op-amps. You have 4 jfets there and they are all horribly priced!

http://www.mantech.co.za/Stock.aspx?Query=n-channel+jfetand

It must be tough living on the other end of the earth from the availability store!

http://www.mouser.com/Semiconductor...JFET/_/N-ax1rs?Keyword=n-channel+jfet&FS=True

 

will the bottom one work, maybe it's cheaper, I'll mail them?

 

I need 8 keys (optimally)... I don't know if I wanna afford it, if I go deep into my safe I might be able to afford the R30 one (R240)... maybe another way? if possible?

 

I finally got Mantech to quit showing me mosfets and jfet input op-amps. You have 4 jfets there and they are all horribly priced!

http://www.mantech.co.za/Stock.aspx?Query=n-channel jfetand

It must be tough living on the other end of the earth from the availability store!

http://www.mouser.com/Semiconductors/Discrete-Semiconductors/JFET/_/N-ax1rs?Keyword=n-channel jfet&FS=True

http://www.fort777.co.za/index.php?...h_result&search_in_description=1&keyword=jfet
My usually more expensive close by supplier: Yebo Electronics (www.fort777.co.za)
Have @R15.20 2N3819 - N Channel JFET http://www.fort777.co.za/index.php?main_page=product_info&cPath=269_456_605_663_664&products_id=5164
R5.27 BF245A N-Channel JFET http://www.fort777.co.za/index.php?main_page=product_info&cPath=269_456_605_663_667&products_id=5879
and then they have jfet op-amps

edit: they have only 1 item of the 2n3819 with 100 on order
and 619 of the BF245A

EDIT: mantech search with "n jfet" produces a higher amount of n channel jfet search results
http://www.mantech.co.za/ProductInfo.aspx?Item=340M0660 -- 2N4393 at R17.26

 

OMG! What have you gotten me into?
I've been reading this for 45 minutes and have so many constraints logged into my mind. Un-availablilty of parts, money, understanding, transportation...
Meanwhile, my real life is demanding my time. I have a computer to fix today, and the owner is so slow she can't change lanes if she has a quarter of a mile to do it.
I don't think I can do this one.

 

OMG! What have you gotten me into?
I've been reading this for 45 minutes and have so many constraints logged into my mind. Un-availablilty of parts, money, understanding, transportation...
Meanwhile, my real life is demanding my time. I have a computer to fix today, and the owner is so slow she can't change lanes if she has a quarter of a mile to do it.
I don't think I can do this one.

No problem my friend... I can take it from here... I'll see what I can do

 

*sigh* how will I? cmartinez, at the beginning you said "God-like" is incorrect, the correct word would be heroic!

 

but thanks for everything so far #12! heroic!

 

No problem my friend... I can take it from here... I'll see what I can do

what is the constraints on the jfet? minimum mA?

 

Chillum, start by reading this article, and you will get a feel of why a jFet is being used in the circuit.

 

There are several other ways to make a constant current source or a ramp. It's just that a jfet is so simple and adjustable. If jfets cost $4 and opamps cost $0.33 use opamps!

It's just that, The last time I bought 2N4416 jfets, I got a roll of 100 for $12.

 

There are several other ways to make a constant current source or a ramp. It's just that a jfet is so simple and adjustable. If jfets cost $4 and opamps cost $0.33 use opamps!

I was wondering about the op-amps cause they ARE way cheaper --- if the result is the same?

 

Chillum, start by reading this article, and you will get a feel of why a jFet is being used in the circuit.

OK learned at least one good thing tonight JFET. good article!

 

OK learned at least one good thing tonight JFET. good article!

Let's now go through what parts you have readily available. You said you have op-amps with you? Of what type and how many?
Do you also have comparators?

 

I was wondering about the op-amps cause they ARE way cheaper --- if the result is the same?

Many ways to skin the cat.
Everything is simple...right after you know how.
Of course an opamp containing hundreds of transistors can replace a single jfet.

 

LM324N op amp x2
LM339N comparator x2
LM358N op amp x2
LM386N-1 audio amp x2

 

LM324N op amp x2
LM339N comparator x2
LM358N op amp x2
LM386N-1 audio amp x2

What about transistors? NPN and PNP... I assume you have no problem finding resistors and caps, and perhaps 555s, right?