HELP - resistors and dip-switch

[allvol]

Yes Sir, Audioguru,

and pin 3 is still unconnected.

 

[audioguru2]

and pin 3 is still unconnected.

 

[allvol]

Yes, I see that now.

 

[Virus]

Guys

Sorry I did not notice the connection in circuit3 posted above where missing, my mistake.

Question still remain, where do I connect the thermistor, in the circuit 3, or in circuit forum lab 3, above ? ? ? ? ?. which ever is the better or more reliable of the two. I do have some 10k thermistors can I use them?

Re: the two resistors in parallel – this site where the circuits come from, on page http://casemods.pointofnoreturn.org/pwm/741.html

In the 2nd  line he states – “using a rotary encoder to set your resistance.”

Does any one have an idea how to use an encoder switch to select resistance, (This could be the answer to the original question)

Thanks once more.

Virus

PS: audioguru, can you please explain to me how to use the "quote" section. Do you select a section you want to use and then hit "Quote", or how?

 

[audioguru2]

Question still remain, where do I connect the thermistor, in the circuit 3, or in circuit forum lab 3, above ? ? ? ? ?. which ever is the better or more reliable of the two. I do have some 10k thermistors can I use them?

In the circuit you posted with the 555 and the opamp, replace R4 or R5 with your 10k thermistor. One position will make the fan speed up when the temperature is colder, so use the thermistor for the other resistor.

audioguru, can you please explain to me how to use the "quote" section. Do you select a section you want to use and then hit "Quote", or how?

Push the Quote button, delete text that you don't want in the quote then end the quote with "" without the " marks. Type your reply below it.
Each time a new sentence is quoted it must begin with "

" and end with "

".

 

[Virus]

In the circuit you posted with the 555 and the opamp, replace R4 or R5 with your 10k thermistor. One position will make the fan speed up when the temperature is colder, so use the thermistor for the other resistor".

audioguru

Thanx will build one and give feed back.

Still no idea on the resistor and the selector thingy. Any ideas ?

Thank you

Virus

 

[Virus]

audioguru

I have built the unit (Reply #19 on: May 12, 2006, 05:44:34 PM ) on a breadboard, 1 ste time not lucky.  The mosfet gets steaming hot instantly, if I clip + 12v to the circuit, with no out put to the led that I connected. I can hear the 555 oscillating. How can I test the opamp to see of it is working.

I have checked and again checked and again checked and …. the wiring can’t find the fault.  Should I rip it all up and redo it? Build it to a PCB ?

Attached photos.

Please help.

Thanks Virus

View attachment 39040

View attachment 39041

 

[audioguru2]

I can't remember how much current your fan draws, but it is a lot more than what the lousy contacts on your breadboard can handle.

What resistor value did you use for the 2N3906 current source?
Is the 555 oscillating?
Does your power supply voltage drop too low when it is loaded, therefore the Mosfet doesn't have enough voltage on its gate to turn on properly?

 

[allvol]

Hi Virus,

If it is any consolation to you, I could not get the circuit to work, either.

 

[Virus]

I can't remember how much current your fan draws, but it is a lot more than what the lousy contacts on your breadboard can handle.

I only had the led connected, no fans at all, wanted to see if the circuit at least is working.

What resistor value did you use for the 2N3906 current source?.

Resistor RF = 90Kohm

Is the 555 oscillating?

Yes, for the 555, I can hear it load enough.

Does your power supply voltage drop too low when it is loaded, therefore the Mosfet doesn't have enough voltage on its gate to turn on properly?

I use the 0 - 30 VDC power supply from this forum, it does not even blink.


audioguru,

is the theory of this circuit good ???,

regarding the post of allvol View attachment 39051

 

[audioguru2]

It is a lousy circuit.
The transistors T1 and T2 aren't needed.
Pin 3 of the 555 can drive a resistor in series with the timing capacitor and the triangle wave on the capacitor can feed the input of the opamp.
I would use a faster, newer opamp or a proper comparator instead of a slow opamp that causes the Mosfet to heat-up. 

View attachment 39052

 

[Virus]

audioguru

Thanks for the circuit update, will build it this weekend and give you feed back.

What should the value of D1 be ? ???

I will bug you a bit more later, I would like to get rid of the RDC 10K and rather use a solid resistor, with a 10 K thermistor, iaw, make it a circuit with a solid predetermined value for the temp sensor to react on.

Thanks

Virus

 

[audioguru2]

What should the value of D1 be?

D1 is not necessary since every Mosfet has a very powerful zener diode inside connected like D1.
You would use an additional very fast diode if the PWM was at a very high frequency.

 

[allvol]

Gosh!

 

[Virus]

allvol

I like say it, "If you are right you are right.", sorry for ignoring you.

 

[allvol]

Hey Virus,

Thanks.

I could not get that circuit to work.... and probably never would.

 

[audioguru2]

I could not get that circuit to work.... and probably never would.

Which circuit? Did you try the circuit I fixed?

I have a DC motor speed control circuit using PWM that works perfectly. I use a dual opamp as an integrator and schmitt trigger to make a triangle wave and use another opamp as a comparator of the triangle wave to the DC setting of a pot like in this circuit.
The 555 circuit that I fixed should work perfectly the same. 

 

[allvol]

We're talking about the original circuit, the one you called lousy.

 

[allvol]

Okay, Virus, maybe this will clear it all up.

In my attachment below, audioguru's version of the 555 as a pulse width generator is compared with the textbook version, as offered by the 555 Timer Pro program from the Schematica web site.

 

[Virus]

Guys

I HAVE FOUND THE PROBLEM, I had the Mosfets supply and drian short-circuited on the breadboard as soon as the circuit switches on. DEAD SHORT INSTANT HEAT.

With that sorted out I have successfully built the circuit in post number 19 (with the MC34071 opamp) and the one in number 34 audioguru’s circuit.

I choose for now to go with the audioguru’s circuit, with less components, and is still on the board. As I got the same results from both circuits.

I have replaced the 4.7k resistor with a 1k resistor, the fans where making a very lousy high pitch sound, then measured with my MM, I get 21kHz, on pin 6 of the 555.

First I replaced R5 with a 10K resistor (because the thermistors value is changing and need a fix value to work from), and adjusted RDC to give an output of 4.5 volts, with the fans just start turning.

Then I replaced R5 with the 10 k thermistor, the output voltage varies with

MC34071-D.pdf