Quest for EE experts: BB2K and others, check this

satanicoo · 04-18-2005, 12:07 PM

Hello there!

Glad to make again this kind of questions on a water-cooling forum, also resourcefull on other subjects!

So what's happening?
I am designing an electrical system for a school project, And i am getting troubles since it is somewhat vague on the ICs we have to use.
They only say "i want something that does this", and they give us some ideas on how to do it and what ICs to use.
So, i will post it here, hoping to have some help from bigben and others electronic
knowledgeable people around.

Introduction:
The students are asked to implement a circuit that controls proportionally light itensity.
The goal is that this circuit reacts inversely to the ambient light. The possible measurable delta should be previously measured with a luximeter (?)

Task 1:
It is pretended that you build an Circuit to power a 24V/24W light. You should use a PWM modulator, sugested CI TL494.
The medium valor of the actuation current should be directly proportional to a variable input tension between 0V and 5V.
The result signal should go trought an optic isolation circuit, using CI TLP521,before it acts on the transistored circuit.

Task 2:
Here you should develop a signal conditioner for an LDR, that will measure the ambient light. The output of the circuit should present a signal between 0V and 5V, correspondent to the max ambient light. Should also be developed, if necessary a linearization circuit. (??)

Task 3:
Now implement a Analog/Digital converter to acoplate to the output of the circuit built in task 2. This should be based on a tipical mount of with CI ADC0801.

Task 4:
Develop a proportional control circuit to stabilize the luminosity at half the maximum luminosity at the Lab.
Thi circuit should be based on operational amplifiers and should have 2 imputs: reference one (a potenciômeter) and the other relative to the total output of the conditioning of the LDR.
The output should be adequated to the actuation of the circuit developed on Task 1. (actuation circuit of the power resistors).

Task 5:
Now interconnect all the circuits. You may need to do some ajustments and you should verify the global functioning, and finally, Some measuremetns snd conclusions should be drawn.
The outputs of the A/D converter are only for visualisation, so they aren't part of the control system.

Task 6:
Here you should develop a D/A converter. It should be based on the CI DAC0800, and the imputs should pass previously on a group of 8 digital buffers, wich will serve as an interface to the digital outputs of a data acquisition board (to use more in front). The output should vary between 0V and 5V and is only for visualization.

Task 7:
Here, an adaptation should be made to the developed system, so that a Pc control can be made.
The acquisition board DT2801 should be used ( to adquire an analog imput and for the exteriorization of 2 outputs, one analog and the other 8 bits digital).
The software to use will be the Labwindows, to program a software to implement the adquisition and control of the luminosity.

UFF! thats it! I will post later the PDFs and what i have done so far.

bigben2k · 04-18-2005, 04:03 PM

I'm familiar with the 494.

The first thing I'd do, is download the data sheets for each chip that you're proposing to use. Print them if you have to; you'll refer to them a lot.

TI's website also has application notes, showing sample circuits.

You should review this project in detail, and figure out what equipment you'll need. An oscilloscope could come in handy here; you should be aware of what signal you can expect at various points throughout the circuit.

This really doesn't seem difficult, and most of the work has been done for you, i.e. the selection of the components. It's just a matter of putting it together.

KnightElite · 04-20-2005, 12:15 AM

I agree, get all the datasheets.

The project seems moderately complicated, but not overly difficult. I'll check back and take a look again later once you have posted the PDFs and suchlike, but all of the individual circuits should be fairly easy. You are taking some kind of EE classes in university I take it?

Anyway, many of the simple circuits required, such as a linearization circuit, will be explained in the datasheet for the IC you are using. Depending on what kind of photodector you are using (or have to use), you may be able to find one that matches all your needs in a single chip. If not, most of them are photodiodes, so the amount of light they receive adjusts the current they transmit through. By running this current accross a resistor, and measuring the voltage drop, you can get your 0-5V output.

satanicoo · 04-25-2005, 10:28 PM

Hi there again guys!

Quote:

Originally Posted by KnightElite

I agree, get all the datasheets.

The project seems moderately complicated, but not overly difficult. I'll check back and take a look again later once you have posted the PDFs and suchlike, but all of the individual circuits should be fairly easy. You are taking some kind of EE classes in university I take it?

Anyway, many of the simple circuits required, such as a linearization circuit, will be explained in the datasheet for the IC you are using. Depending on what kind of photodector you are using (or have to use), you may be able to find one that matches all your needs in a single chip. If not, most of them are photodiodes, so the amount of light they receive adjusts the current they transmit through. By running this current accross a resistor, and measuring the voltage drop, you can get your 0-5V output.

Yes, i am taking a EE class in university, and things are starting to get complicated

So you are saying that the linearization circuit should be a IC?
This LDR varies Resistance directly with the amout of light, i have decided to put it feeding a transistor to limit the current that pass trought it, and reduce heating.
This is working quite farelly well, however, it is not linear, showing an inverse exponencial curve on tension (good english anyone?).

We decided to let it stay non-linear for now, and move on to task 3 (we are getting late

)
So, me and my friend are stuck at task 3, we are still trying to understand how the hell this IC works ( IC ADC0801).

If you guys can give us some imput on the linearization circuit and, on this decoder, we would be thankfull to you guys

.

Here's the PDF's:
Tl494
TLP521
ADC0801 A/D Converters
DAC0800
DT2801 (unnecessary i think)

That's it. Tomorrow i'll post the schematics of what we made so far. Cya!

lukr · 04-27-2005, 05:23 PM

whats your question about the AD converter?
Just a quick info: It converts analog signals (one voltage in this case) to digital signals. Connect a known voltage to the reference-input pin (Vref). Connect the voltage you want to know to the Vin(+) pin, and Vin(-) to ground. And shows Vin/Vref on the digital output pins (you know binary numbers?).
(DB0..DB7 pins are the digital outputs in that chip.
MSB=Most significant bit, LSB=least significant bit.
1=high=voltage on pinX is about 5V; 0=low=voltage on pinX is about 0V.)

Some examples: if Vin=Vref the out (DB0..DB7) will be 11111111 (8bit ADC) , if Vin=0, out will be 00000000. If Vref=5V, and Vin=3.46V (Vin/Vref=0.692) the digital output will be close to 0.692*255=177=10110001. Maybe not exactly, because of some electrical noise or like, but accuracy is not realy important now i think.

For a quick test, look@chapter "Testing the A/D converter", pg23-24 in the datasheet.

satanicoo · 04-27-2005, 07:27 PM

Omg you made it simple! thanks!

KnightElite · 04-28-2005, 05:46 PM

I'm not trying to say your linearization circuit should be an IC. I have never used an LDR, but I have used thermisters, and for the ones I have used, the datasheet for the thermister explains how you should set up a resistor network for linearizing it over the specific temperature range you want to use. I was assuming the LDR datasheet would have something similar.

satanicoo · 04-29-2005, 07:26 AM

Humm... a datasheet for a LDR?
Never heard of it, im gonna search for one, or google for a linearization circuit!

BTW, here's Task 1 work:

There's a problem here: The control voltage range varies between 0-2.5V, and it must be between 0-5V, I will modify it with an AMPOP with a gain of 1/2, efectively reducing the 0-5V to 0-2.5V and then I should have completed this task.

KnightElite · 05-02-2005, 10:14 PM

If by that you meant use an Op Amp with a gain of two to double the control voltage, then that should work. As to datasheets:

http://www.datasheetarchive.com/data...16/165739.html

There's one for an LDR, I don't know which LDR you have. However, it does not seem to have a linearization circuit described on it. But in any case, basic linearization principles apply, and if you can't figure it out, I will go dig out my lab manual and find the relevant data about linearizing thermisters

.

satanicoo · 05-05-2005, 03:17 PM

Can someone give me a hand with DAC0800 like lukr gave? I'm stuck at task 6 now because of that one...

lukr · 05-06-2005, 02:05 PM

in short a Digital to Analog converter converts digital signali to analoge voltage or current.
In this case the output is current, but the datasheet shows how to convert the current to voltage.
Again, just look in the datasheet, and use one of the "tipical applications" diagrams.

For testing, connect the ADC's 8 output bits to the DAC's 8 input bits, and if everything is OK, the output voltage from the DAC should be the same as the input voltage to the ADC.

satanicoo · 05-07-2005, 08:08 PM

20 V point to point? Always positive?
I think it reverses!!

Maybe not :|

How about getting an output of 0-5 volts?

04-18-2005, 12:07 PM	#1
satanicoo Cooling Savant Join Date: Nov 2002 Location: portugal Posts: 635	Quest for EE experts: BB2K and others, check this Hello there! Glad to make again this kind of questions on a water-cooling forum, also resourcefull on other subjects! So what's happening? I am designing an electrical system for a school project, And i am getting troubles since it is somewhat vague on the ICs we have to use. They only say "i want something that does this", and they give us some ideas on how to do it and what ICs to use. So, i will post it here, hoping to have some help from bigben and others electronic knowledgeable people around. Introduction: The students are asked to implement a circuit that controls proportionally light itensity. The goal is that this circuit reacts inversely to the ambient light. The possible measurable delta should be previously measured with a luximeter (?) Task 1: It is pretended that you build an Circuit to power a 24V/24W light. You should use a PWM modulator, sugested CI TL494. The medium valor of the actuation current should be directly proportional to a variable input tension between 0V and 5V. The result signal should go trought an optic isolation circuit, using CI TLP521,before it acts on the transistored circuit. Task 2: Here you should develop a signal conditioner for an LDR, that will measure the ambient light. The output of the circuit should present a signal between 0V and 5V, correspondent to the max ambient light. Should also be developed, if necessary a linearization circuit. (??) Task 3: Now implement a Analog/Digital converter to acoplate to the output of the circuit built in task 2. This should be based on a tipical mount of with CI ADC0801. Task 4: Develop a proportional control circuit to stabilize the luminosity at half the maximum luminosity at the Lab. Thi circuit should be based on operational amplifiers and should have 2 imputs: reference one (a potenciômeter) and the other relative to the total output of the conditioning of the LDR. The output should be adequated to the actuation of the circuit developed on Task 1. (actuation circuit of the power resistors). Task 5: Now interconnect all the circuits. You may need to do some ajustments and you should verify the global functioning, and finally, Some measuremetns snd conclusions should be drawn. The outputs of the A/D converter are only for visualisation, so they aren't part of the control system. Task 6: Here you should develop a D/A converter. It should be based on the CI DAC0800, and the imputs should pass previously on a group of 8 digital buffers, wich will serve as an interface to the digital outputs of a data acquisition board (to use more in front). The output should vary between 0V and 5V and is only for visualization. Task 7: Here, an adaptation should be made to the developed system, so that a Pc control can be made. The acquisition board DT2801 should be used ( to adquire an analog imput and for the exteriorization of 2 outputs, one analog and the other 8 bits digital). The software to use will be the Labwindows, to program a software to implement the adquisition and control of the luminosity. UFF! thats it! I will post later the PDFs and what i have done so far. __________________ back.

04-18-2005, 04:03 PM	#2
bigben2k Responsible for 2% of all the posts here. Join Date: May 2002 Location: Texas, U.S.A. Posts: 8,302	I'm familiar with the 494. The first thing I'd do, is download the data sheets for each chip that you're proposing to use. Print them if you have to; you'll refer to them a lot. TI's website also has application notes, showing sample circuits. You should review this project in detail, and figure out what equipment you'll need. An oscilloscope could come in handy here; you should be aware of what signal you can expect at various points throughout the circuit. This really doesn't seem difficult, and most of the work has been done for you, i.e. the selection of the components. It's just a matter of putting it together. __________________ WBTA (Water Block Testing Alliance) Nordic Hardware WC 101

04-20-2005, 12:15 AM	#3
KnightElite Cooling Savant Join Date: Sep 2002 Location: Saskatoon, Saskatchewan Posts: 294	I agree, get all the datasheets. The project seems moderately complicated, but not overly difficult. I'll check back and take a look again later once you have posted the PDFs and suchlike, but all of the individual circuits should be fairly easy. You are taking some kind of EE classes in university I take it? Anyway, many of the simple circuits required, such as a linearization circuit, will be explained in the datasheet for the IC you are using. Depending on what kind of photodector you are using (or have to use), you may be able to find one that matches all your needs in a single chip. If not, most of them are photodiodes, so the amount of light they receive adjusts the current they transmit through. By running this current accross a resistor, and measuring the voltage drop, you can get your 0-5V output. __________________ Can anyone else here say that they have a watercooled monster that's 45" tall?

04-27-2005, 07:27 PM	#6
satanicoo Cooling Savant Join Date: Nov 2002 Location: portugal Posts: 635	Omg you made it simple! thanks! __________________ back.

04-28-2005, 05:46 PM	#7
KnightElite Cooling Savant Join Date: Sep 2002 Location: Saskatoon, Saskatchewan Posts: 294	I'm not trying to say your linearization circuit should be an IC. I have never used an LDR, but I have used thermisters, and for the ones I have used, the datasheet for the thermister explains how you should set up a resistor network for linearizing it over the specific temperature range you want to use. I was assuming the LDR datasheet would have something similar. __________________ Can anyone else here say that they have a watercooled monster that's 45" tall?

04-27-2005, 05:23 PM	#5
lukr Cooling Neophyte Join Date: Dec 2003 Location: Hungary Posts: 23	whats your question about the AD converter? Just a quick info: It converts analog signals (one voltage in this case) to digital signals. Connect a known voltage to the reference-input pin (Vref). Connect the voltage you want to know to the Vin(+) pin, and Vin(-) to ground. And shows Vin/Vref on the digital output pins (you know binary numbers?). (DB0..DB7 pins are the digital outputs in that chip. MSB=Most significant bit, LSB=least significant bit. 1=high=voltage on pinX is about 5V; 0=low=voltage on pinX is about 0V.) Some examples: if Vin=Vref the out (DB0..DB7) will be 11111111 (8bit ADC) , if Vin=0, out will be 00000000. If Vref=5V, and Vin=3.46V (Vin/Vref=0.692) the digital output will be close to 0.692*255=177=10110001. Maybe not exactly, because of some electrical noise or like, but accuracy is not realy important now i think. For a quick test, look@chapter "Testing the A/D converter", pg23-24 in the datasheet.

04-29-2005, 07:26 AM	#8
satanicoo Cooling Savant Join Date: Nov 2002 Location: portugal Posts: 635	Humm... a datasheet for a LDR? Never heard of it, im gonna search for one, or google for a linearization circuit! BTW, here's Task 1 work: There's a problem here: The control voltage range varies between 0-2.5V, and it must be between 0-5V, I will modify it with an AMPOP with a gain of 1/2, efectively reducing the 0-5V to 0-2.5V and then I should have completed this task. __________________ back.

05-02-2005, 10:14 PM	#9
KnightElite Cooling Savant Join Date: Sep 2002 Location: Saskatoon, Saskatchewan Posts: 294	If by that you meant use an Op Amp with a gain of two to double the control voltage, then that should work. As to datasheets: http://www.datasheetarchive.com/data...16/165739.html There's one for an LDR, I don't know which LDR you have. However, it does not seem to have a linearization circuit described on it. But in any case, basic linearization principles apply, and if you can't figure it out, I will go dig out my lab manual and find the relevant data about linearizing thermisters . __________________ Can anyone else here say that they have a watercooled monster that's 45" tall?

05-05-2005, 03:17 PM	#10
satanicoo Cooling Savant Join Date: Nov 2002 Location: portugal Posts: 635	Can someone give me a hand with DAC0800 like lukr gave? I'm stuck at task 6 now because of that one... __________________ back.

05-06-2005, 02:05 PM	#11
lukr Cooling Neophyte Join Date: Dec 2003 Location: Hungary Posts: 23	in short a Digital to Analog converter converts digital signali to analoge voltage or current. In this case the output is current, but the datasheet shows how to convert the current to voltage. Again, just look in the datasheet, and use one of the "tipical applications" diagrams. For testing, connect the ADC's 8 output bits to the DAC's 8 input bits, and if everything is OK, the output voltage from the DAC should be the same as the input voltage to the ADC.

05-07-2005, 08:08 PM	#12
satanicoo Cooling Savant Join Date: Nov 2002 Location: portugal Posts: 635	20 V point to point? Always positive? I think it reverses!! Maybe not :\| How about getting an output of 0-5 volts? __________________ back.

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