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 Posted: Mar 02, 2009 - 02:57 AM |
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Joined: Dec 30, 2004
Posts: 8769
Location: Melbourne,Australia
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| Why have the voltages gone west? There's something wrong somewhere! I doubt adding a 10K resistor would cause enough current to flow to smoke a little transistor. |
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Posted: Mar 02, 2009 - 04:31 AM |
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Joined: Feb 29, 2008
Posts: 119
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Kartman wrote:
As I previously said, add a pulldown resistor from base to ground (emitter). Try about 10k. If that doesn't work, you've got a suspect transistor or it's wired in the wrong way.
Ok, by "emitter" do u mean to ground the emitter pin? I've already done that but without the 10k. I was grounding the BASE pin, not the Emitter pin... Is that what you wanted me to do? Ground the Base or Emitter?
David |
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Posted: Mar 02, 2009 - 05:52 AM |
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Joined: Dec 30, 2004
Posts: 8769
Location: Melbourne,Australia
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| The instruction was to connect a 10k resistor between the base and the emitter, then something went wrong. My crystal ball isn't working too well today. Sit down and work through the problem logically. Give yourself a chance to solve the problem - using forums is way too easy and a good way to wear out your welcome. |
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Posted: Mar 02, 2009 - 09:50 PM |
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Joined: Feb 29, 2008
Posts: 119
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Ok, i re-soldered the 10k and it seems to work when i provide 5v on the pin BUT it doesn't trigger back off once i take away the 5v?
Base without 5v: 8.48v
Base with 5v: 5.87v
David |
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Posted: Mar 02, 2009 - 10:48 PM |
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Joined: Dec 30, 2004
Posts: 8769
Location: Melbourne,Australia
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| Well, I think you have a problem. Try another transistor and ensure that you wire it correctly. Are you sure the transistor in question is wired EBC? Or is it BCE? You can check with a multimeter as you should measure a diode between B & E, B & C. |
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Posted: Mar 03, 2009 - 02:05 AM |
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Joined: Feb 29, 2008
Posts: 119
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Posted: Mar 03, 2009 - 02:15 AM |
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Joined: Dec 30, 2004
Posts: 8769
Location: Melbourne,Australia
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| BC548s are EBC - as you've shown. If you've got >0.8V on the base, then something is wrong. Do I have to repeat myself? |
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Posted: Mar 03, 2009 - 02:24 AM |
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Joined: Feb 29, 2008
Posts: 119
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But im not getting 0.8v on the base??
Quote:
Base without 5v: 8.48v
Base with 5v: 5.87v
David |
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Posted: Mar 03, 2009 - 02:31 AM |
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Joined: Feb 29, 2008
Posts: 119
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And i see that i had the wrong PDF looking at the pin out.... I'll re-wire it and see what goes on.
Thanks for the correction.
David |
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Posted: Mar 03, 2009 - 02:51 AM |
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Joined: Feb 29, 2008
Posts: 119
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Ok i re-wired it and the relay comes on when i supply the 12v to it. I get the these values:
Base: 0.84v
Base w/ 10k: 1.17v
collector: 0.01v
And yes, i know somethings wrong.
David |
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Posted: Mar 03, 2009 - 03:54 AM |
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Joined: Dec 30, 2004
Posts: 8769
Location: Melbourne,Australia
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At a guess, I'd say the transistor is fried. It seems against the laws of physics that the base voltage rises with the 10K resistor connected.
1. Do a Google and find out how transistors work
2. Get yourself a handful of transistors to play with
3. Try the experiments again.
Problem should be solved, if not, you have made a process error.
I'd suggest you use a transistor other than the BC548. Its collector current is a bit low. Maybe something like a BD139/639 or a 2N3904 depending on what side of the Atlantic you're on. |
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Posted: Mar 03, 2009 - 04:37 AM |
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Joined: Feb 29, 2008
Posts: 119
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Its a brand new one i used so i could rule out the fried part.
I know how transistors work.
All i have is:
Small Signal Transistors NPN 30V 100mA HFE/8
Did u want me to take out the 1k resister and replace it with the 10k? Currently i have BOTH in place.
David |
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Posted: Mar 03, 2009 - 05:38 AM |
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Joined: Dec 30, 2004
Posts: 8769
Location: Melbourne,Australia
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Quote:
I know how transistors work.
From what you're telling me, your transistor is not working, so that would suggest you don't know how they work!
Quote:
Small Signal Transistors NPN 30V 100mA HFE/8
So what are these magic transistors? with a HFE of /8?? they don't have much gain. Are they actual BC548s or something like a BC548 or maybe something we don't actually know what they are?
Quote:
Did u want me to take out the 1k resister and replace it with the 10k? Currently i have BOTH in place.
Why would I want that? I don't see what that would acheive. You can try, but I think that would be clutching at straws. There's a fundamental problem that hasn't been addressed, so short of voodoo magic, I can't suggest much else. |
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Posted: Mar 03, 2009 - 08:49 PM |
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Joined: Feb 29, 2008
Posts: 119
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Here is the picture of my board...
I'm confident that everything is connected correctly.
David |
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Posted: Mar 03, 2009 - 10:27 PM |
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Joined: Dec 30, 2004
Posts: 8769
Location: Melbourne,Australia
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If everything is correct, why is it not working? I've lost count of the times people have sworn things were wired correctly, but the system wasn't working only to find that it wasn't wired correctly.
Let's assume you have wired it correctly, what does that leave?
1. transistor - I still don't know what exact transistor you are using. You haven't shown the results of the multimeter test I suggested, so I'd say the transistor is a prime suspect.
2. resistors - correct value?
3. Relay - not likely as it seems to do what it is told.
4. wiring
David, I admire your persistance, but showing me pictures and giving me half information is not going to solve your problem. We're talking about a very simple circuit, so the problem must be very simple. I dare say once you've found the problem, you're going to be red-faced as you've made certain claims that will be proven to be false. Stop guessing and apply a logical approach to the problem. There's no magic here. |
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Posted: Mar 03, 2009 - 11:59 PM |
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Joined: Feb 29, 2008
Posts: 119
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Here's all the information on the transistor:
Quote:
Manufacturer: Fairchild Semiconductor
Product Category: Bipolar Transistors
Product: Bipolar Small Signal & Power
Transistor Polarity: NPN
Mounting Style: Through Hole
Package / Case: TO-92
Configuration: Single
Maximum Operating Frequency: 100 MHz (Min)
Collector- Emitter Voltage VCEO Max: 25 V
Emitter- Base Voltage VEBO: 6 V
Maximum DC Collector Current: 1.5 A
Power Dissipation: 1000 mW
DC Current Gain hFE Min: 120 @ 100mA @ 1V
Packaging: AMMO
Continuous Collector Current: 1.5 A
Maximum Operating Temperature: 150 C
I tested the transistor with my multimeter and it tells me 058.
Testing it i get:
B (led lead)/E (ground) = LED lights up
B (led lead)/C (ground) = LED lights up
And i was following this diagram to test the above:
The resister(s) are correct:
1k = Brown/Black/Red/Gold
10k = Brown/Black/Orange/Gold
Relay works because, yes, it clicks.
David |
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Posted: Mar 04, 2009 - 12:13 AM |
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Joined: Dec 30, 2004
Posts: 8769
Location: Melbourne,Australia
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David,
Where is the part number of the transistor?
Your results for the transistor test are incomplete - there should be four outcomes, not two. I can only assume your multimeter has a transistor test feature, thus the magic figure of 058 which means F/A to me.
You really are relying on my magic powers of perception! You expect a lot. |
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Posted: Mar 04, 2009 - 12:47 AM |
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Joined: Feb 29, 2008
Posts: 119
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The transistor part number: SS8050CTA
Ok, i replaced all the parts and started over.
Good news. No more click when i supply the 12v to the relay but i am still not getting it to open once i supply the 5v.
Base: 4.60v
Collector: 8.84v
Between coils: Right side: 8.83v Left side: 12.09v
The forums are here so others can help. I have done my homework and presented this all to those in hopes someone could find an error in it. Just like with programming, 2 heads are better than one at finding the smallest mistake that the programmer would probably never see since he wrote the thing in the first place. Same principle here.
David |
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Posted: Mar 04, 2009 - 04:31 AM |
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Joined: Dec 30, 2004
Posts: 8769
Location: Melbourne,Australia
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David, again you are scarce with vital information. Just so we're on the same page with the transistor:
http://www.fairchildsemi.com/ds/SS%2FSS8050.pdf
Look at figure 4 - a nice little graph. How does this relate to what you're seeing?
Quote:
Good news. No more click when i supply the 12v to the relay but i am still not getting it to open once i supply the 5v.
Base: 4.60v
Collector: 8.84v
Between coils: Right side: 8.83v Left side: 12.09v
So what changed? If it was wired correctly as you assert, the result should've been the same.
What does 'between coils' mean? We have only one coil as far as I'm aware. What do you do to get these measurements?
Quote:
The forums are here so others can help. I have done my homework and presented this all to those in hopes someone could find an error in it. Just like with programming, 2 heads are better than one at finding the smallest mistake that the programmer would probably never see since he wrote the thing in the first place. Same principle here.
Sorry David, you haven't done your homework - all you've done is to assert how right you are. If you knew how transistors worked, you would've solved the problem for yourself. If you wired it correctly the first time, why do you get different results when you wire it up again? I'd suggest one is a little more humble when he is receiving assistance for free especially when you're doing little to help your sorry ass.
Draw your test setup, then write in the voltages at the various points. At least then we can be clear as to what you mean.
Others: feel free to chime in! |
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Posted: Mar 09, 2009 - 08:48 PM |
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Joined: Feb 29, 2008
Posts: 119
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OK, i went to radio shack and got a butt load of transistors 
It seems the 2n4404 (http://www.fairchildsemi.com/ds/2N%2F2N4401.pdf) works fine with a 1k resistor. However, i still am having the problem with no 12v coming out from the relay!
The collector has 12v when 5v is not connected and 0.03v when connected.
Yes, i hear it click just fine.
The relay pin out looks like this: http://www.components.omron.com/compone ... BFF8525...
I have it hook like so:
Pin 2 = 12v
Pin 5 = collector pin
Pin 3 = (should have 12v coming out?)
Pin 4 = 12v
I've also tried this:
Pin 2 = 12v
Pin 5 = collector pin
Pin 3 = 12v
Pin 4 = (should have 12v coming out?)
What am i doing wrong????
David |
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