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Re: Need help with a circuit again

Posted: Tue Oct 16, 2018 5:43 pm
by evahle
1moldmaker wrote:
Mon Oct 01, 2018 5:52 am
thanks, here is a link to my circuit https://drive.google.com/file/d/1xk6dTF ... sp=sharing
I thought I'd try to upload your schematic directly here.

Re: Need help with a circuit again

Posted: Mon Oct 22, 2018 6:47 am
by 1moldmaker
I found if I take out the 10K (R4) resistor the circuit works better, but the only problem that I have is when I turn the trim pot down to a lower resistance I burn up the trim pot. What I was thinking was putting a resistor parallel with the trim pot but I wouldn't know that resistance that I should use,

Re: Need help with a circuit again

Posted: Mon Oct 22, 2018 7:09 am
by dyarker
Putting a resistor in parallel with the pot will not save the pot. Is just passes more current around the pot. The excessive current through the pot at low setting stays the same.

I left the 10K in to give the original 2 seconds when pot at zero. I do not know what size (in Watts) your pot is But ifyou change 10K to 1K, 1.5K, 2.2K ... 5.4K (or other standard resistance) smaller than 10K should give what you want. 1K or more should protect the pot (depending on power rate of pot)

Cheers,

Re: Need help with a circuit again

Posted: Mon Oct 22, 2018 7:44 am
by dyarker
Looking at it again -

What else have you done?

R3 times the gain of Q1 should have prevented pot burn-out.

What colors are the bands on R3?

Re: Need help with a circuit again

Posted: Tue Oct 23, 2018 1:41 pm
by 1moldmaker
Well I kind of made some changes to the circuit, I took out the 1K resistors and I am using incandescent light bulbs in stead of LED's, also I am running the circuit at 12 to 14 volts, and I am using TIP122 darling transistors instead of 2n3904.

Re: Need help with a circuit again

Posted: Tue Oct 23, 2018 3:22 pm
by dyarker
Without R3 the circuit is not a schmitt trigger anymore. The Q1 base resistance to negative supply is like 1 or 2 Ohms (bad!).

With R3 the base resistance is like 50K to 100K (no burnt pots). R3 being "shared" with Q2 causes the "snappy" switch between which transistor is on.

It is better to put original circiut back, and put "heavier" transistors where the LEDs are. They drive the bulbs.

How much current do the bulbs need?

Re: Need help with a circuit again

Posted: Tue Oct 23, 2018 3:39 pm
by 1moldmaker
the light bulbs are14v at 0.22a, I thought the R3 resistor was for the other led.

Re: Need help with a circuit again

Posted: Tue Oct 23, 2018 6:22 pm
by dyarker
try to attach schematic, get logged out

Re: Need help with a circuit again

Posted: Tue Oct 23, 2018 6:32 pm
by 1moldmaker
its like you have to log in twice then you post a reply

Re: Need help with a circuit again

Posted: Wed Oct 24, 2018 4:17 am
by dyarker
Schmidt2LEDs2.png
Last night 20 logins, nothing; today 2 like you said.

Re: Need help with a circuit again

Posted: Wed Oct 24, 2018 7:18 am
by 1moldmaker
Thanks, do you think I can bread board this schematic using 2n3906 transistors, I would have to wait a week to get the tip127's

Re: Need help with a circuit again

Posted: Wed Oct 24, 2018 7:30 am
by dyarker
sure! the bulbs will be too much current for 2N3906s, so use LEDs and 1K resistors.

Re: Need help with a circuit again

Posted: Wed Oct 24, 2018 10:41 am
by Janitor Tzap
Just a quick comment......

I've seen this type of circuit in one of my old Transistor Circuit's Books.
It will work with Model: Eiko 222 2.2V .25Amp light bulbs.


Signed: Janitor Tzap

Re: Need help with a circuit again

Posted: Thu Oct 25, 2018 10:48 am
by 1moldmaker
Just wondering could this circuit be made with mosfets other than using the 2n3904's, and eliminating the tip127's I have some irf644 mosfets laying around, that way I could I go with a higher voltage with my light bulbs?

Re: Need help with a circuit again

Posted: Fri Oct 26, 2018 12:27 am
by Leo Hathaway
I think you must know the component very well and then you may have a test to check it.

So the basic knowledge of your components in circuit you must know, here is the part https://www.kynix.com/Blog/316.html, also you must keep your circuit is correct first.

cheers.