# Circuit Explanation Needed.

Discussion in 'General Electronics Chat' started by sonic007, Feb 29, 2012.

1. ### sonic007 Thread Starter New Member

Feb 26, 2012
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0
I am a beginner Electronics enthusiastic and I am trying to build a circuit and I kind of know how to go about assembling the circuit but I do not understand purpose of some of components in the circuit. I have attached an image of the circuit for your reference. http://www.futurekit.com/2009/manual/future/eng/PDF_FK9/fk945e-1.pdf

The circuit is "Digital Temperature Controller.

The Electronic kit seller did not provide a clear and through explanation of the circuit. Can someone help me with the explanation of the circuit. For example

- The Purpose of the Relay , npn Transistor (TR2 C458) , LED1 ?

-The Purpose of the combination ( R1, C1 , C2) on the left top part of the circuit ?

-The Purpose of the combination ( TR1 C9013, ZD1 5V1,C3,R23,D1 4001, C4 ) on the right top part of the circuit ?

Also , the document explains that "Jumping J1" is used as operation of relay.
UnJumped - relay will be working at the lower temp and stop working at the higher temp.

How can I make a change to the circuit so that it just reads tempreture.

Thank you So much.

Last edited: Feb 29, 2012
2. ### ErnieM AAC Fanatic!

Apr 24, 2011
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The part of the schematic where the actual AC load is controlled isn't shown. Look at the pictoral next page, there are contactors inside the relay to control the AC.
R1 & C1 form a "power on clear" circuit: when power is first applied this point stays low for a bit to signal IC2 to do a reset.
C2 is a +5V voltage filter.
Drawn bass ackwards, it's a voltage regulator. 12V in/5V out.
Don't use the AC socket. (It should be reading temperature anyway.)
You're welcome.

And welcome to the forums!

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3. ### BSomer Member

Dec 28, 2011
433
107
For a little clarification: TR2 is used to control the relay. which controls the mains voltage to the heating/ac unit being controlled. LED1 just shows the state of the relay on/off. In the schematic it is connected to the 12VDC coil of the relay. The reason the transistor is used is because the uC (ATtiny2313) cannot directly drive the relay. The relay works with 12 VDC and the uC works with 5.5VDC max.

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4. ### @android Member

Dec 15, 2011
178
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Most of the things are clear now. So just to display temp you can skip components from transistor connected 'B4' pin.

• ###### skip.JPG
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5. ### BSomer Member

Dec 28, 2011
433
107
Yes. That will get you just the temp reading. Then if you so desire at a later date, you can add the capability to control something based on the temp.

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6. ### @android Member

Dec 15, 2011
178
10
Yeah BSomer . Playing with temp controller is fun. I had done temp controller as a mini project in my college. I had demonstrated it with small fan. Displaying temp on LCD continuously and setting off alarm+LED(blinking)+fan. It was fun!

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7. ### sonic007 Thread Starter New Member

Feb 26, 2012
11
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I am really new to this site and I am flabbergasted by the swift and intuitive responses which I received. Thank you so ...so much all.

My second question is , the kit comes with a PIC that is already programmed and the CODE is unfortunately is locked and can not be accessed and modified.

The product description pamphlet included in the kit does not indicate what type of seven segment display it is. (common cathode/common anode). I have searched the Internet using the "serial" printed on the side of the seven segment display but to no avail; could not find a schematic or data sheet for it.

Secondly , I have purchased a pickit3 In-Circuit Debugger/Programmer. I don't know if the PIC (IC2 attiny2313) can be programmed using pickit3 or arduino.

If any one of you can kindly provide me with a CODE that I can run on pickit3 or arduino I would greatly appreciate it.

All I want is just for the circuit to read a body temperature with out no restriction. ( when temp<25 circuit stops working ..etc..)

8. ### BSomer Member

Dec 28, 2011
433
107
The ATtiny is an Atmel device and to my knowledge cannot be programmed with the PICKit. The PICKit is designed for Microchips Pic line of mcu's.

The Arduino can be used as a ICSP for the Atmel AVR series mcu's (ATtiny). I seen a tutorial once on how to do it, though I cannot remember where. It might have been on www.adafruit.com , not certain.

If yo go to the Arduino website you can find many example codes and tutorials. Another decent site for tutorials on the arduino is: http://tronixstuff.wordpress.com/tutorials/

--Brian

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9. ### thatoneguy AAC Fanatic!

Feb 19, 2009
6,349
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The code is pretty straightforward, some temp sensors send out the temperature at 12 bit resolution over SPI or I2C.

The question is if you want an "In Ear IR" sensor, or an under tounge probe, or basically, where you'd like to measure temp, it varies and you need to apply an offset or multiple to each type of measurement, which you figure out by measuring in different conditions and compare against a "known good" temp reader.

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10. ### sonic007 Thread Starter New Member

Feb 26, 2012
11
0
Dear thatoneguy,

Thank you for your response. You've mentioned that the code is pretty straightforward, You seem like you are background PIC programming. Would you be kind enough to provide a code that I can run and make the circuit read and display body temperature.

Thank you

11. ### sonic007 Thread Starter New Member

Feb 26, 2012
11
0
Hello ErnieM,

12. ### sonic007 Thread Starter New Member

Feb 26, 2012
11
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I want measure the body temperature of a person through a finger tip by just touching the temp sensor.

13. ### sonic007 Thread Starter New Member

Feb 26, 2012
11
0
Hello android,

When you say to just skip the circuit part you have attached, does that mean pin 16 will be left unused ?

14. ### ErnieM AAC Fanatic!

Apr 24, 2011
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1,827
The AC socket does not appear in the schematic. It only appears in the "NO. 1" drawing top of 2nd page. As drawn, the relay will close energising the AC OUT socket if the AC IN plug is inserted into a wall outlet. (You could also use that relay for switching a different voltage shoud you wish, such as using the 12V power to power another device.)

The jumper controls how the relay is energised. If you don't use the relay then that jumper does not matter to you. The display should continue to display whatever temperature the 18B20 sensor is sensing.

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15. ### sonic007 Thread Starter New Member

Feb 26, 2012
11
0
Hello ErnieM,

One more question, on the kit's manual the Three "7 segment displays" are shown connected as one block (in figure 1) http://www.futurekit.com/2009/manual/future/eng/PDF_FK9/fk945e-1.pdf

I am kind of unsure as to how to connect them. My breadboard is as shown in the image attached.

http://s1164.photobucket.com/albums/q574/sonic0007/?action=view&current=IMG_0001.jpg

Also , if you , or anybody else who reads this message, can help me with the programming code I would greatly appreciate it.

I will wait for your response.

16. ### thatoneguy AAC Fanatic!

Feb 19, 2009
6,349
730
Do you already have a PIC and PICKit2 or PICKit 3 for programming?

Versed in either PIC Assembly, or a compiler you are comfortable with?

What size are you shooting for on this?

Measuring the temp of a finger/hand/foot will get you a 5 degree error, +/- You need to measure as close to the "core" as you can, armpits work well, ears have their own dangers if using a probe, mouths are wet, etc.

The design needs to be comfortable for the user as well.

If you are looking at a touch-free IR method as the new ear thermometers are, you can't really buy the sensor for cheaper than buying a few of the pre-made themometers and adding your own stuff to it. IR Ear thermometers get close when pointed at an armpit.

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17. ### sonic007 Thread Starter New Member

Feb 26, 2012
11
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hello thatoneguy,

I recently bought pickit3 from digikey. I am measuring a temperature of a finger by holding the IC1 18B20 temperature sensor.

Any suggestion ?

18. ### sonic007 Thread Starter New Member

Feb 26, 2012
11
0
hello thatoneguy,

I must also add that I have arduino.

19. ### thatoneguy AAC Fanatic!

Feb 19, 2009
6,349
730
Add a 16x1 LCD display to it, build it in "gumstick" form, run the 3 wires through a non-conductive sheath (heat shrink with stiff solid wire) so the transistor can be put in armpit, measurement goes for 15 seconds or until stable, then beeps.

How to do it: Get the 1 wire Dallas temp sensor or whatever sensor you are currently using. I'd suggest one with a digital output (1 wire or SPI), so noise is less of an issue vs. measuring an analog voltage, as the wires to the probe make great antennas.

Then write the code. When reset is hit, initialize LCD, and read temp, once temperature is stable, display on LCD and beep. Wait 30 seconds, go back to low power sleep again. A CR2032 coin cell would power this for a long time if not used continually.

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20. ### sonic007 Thread Starter New Member

Feb 26, 2012
11
0
Dear thatoneguy, the "temp sensor circuit" requires a 12v and I also have another "heart pulse" circuit which requires a 5v. My ultimate goal is to have both circuit on one breadboard and display body temp and heart pulse. But how can I use just one input voltage (say 12V,5V or 9V) ?