7805 Strange Issue

[Mark Linehan]

Okay, obviously I have made numerous mods in the past, but when it came to 5v mods I almost always used the 3 pin packages for my regulators as I always try to use the sturdiest and highest rated switches I can. Well, I have not used a 7805 since one of my first mods, and now that I used one again, I am getting the strangest action from my circuit. I am sure that there is something incredibly stupid that I am missing here, but I can not think of what it is. I am a firm believer in extra sets of eyes seeing extra things, so please take a look-see at my circuit and tell me what could be causing my LED to stay on constantly? I have it wired with a 470 ohm resistor in-line going from pin 2 to pin 3 (Vo to Ground) and I thought that when the fire switch was open there was no voltage from Vo. I mean, the atty does not fire until I press the switch. The LED is lighting up pretty well. I put my meter across the LED and it is reading 3.04v so this is not just some sort of minor voltage leak or anything.

Here is a hand drawn image of my circuit. I would post an image of the circuit but it would not help as I compressed everything down to as tight of a fit as I possibly could.

Oh and I checked for shorts and continuity issues and there appear to be none. My soldering skills are finally getting back in shape as I re-learned the 3 most important things for soldering well. 1. Keeping your tip clean and tinned 2. Using flux 3. Using clip on heat sinks


I have a feeling someone is going to tell me I have something in backwards.

PS. A quick thank you to those 14 members now who have joined my do it yourself forums. Thank you for spreading the word and I am re-inviting all of my friends from ECF to check it out. This is not an E-Cigarette forum. These are forums covering every type of DO IT YOURSELF type interest/hobby out there and I am adding new ones whenever someone asks for one. and if they know a lot about it I invite them to moderate it for me. Sorry about the commercial.

 

[kjj]

Er, most 7805 chips are 3 pin devices. Is that more like a Fairchild KA378R05?

Double check the pinout on your regulator. I think it might be backwards.

 

[Gummy Bear]

@ Mark
I don't think you have a drawing for a 7805.
A 7805 has 3 pins
1: v in
2: Ground
3: regulated v out

(Edited to remove WAG)

If it is one of the 4 pin regs from MadVapes here is his drawing

 

[AttyPops]

Your drawing shows a 4 pin regulator.

1) In
2) Out
3) ground
4) control

Ditto on Gummy's post (the diagram).... now the resistors:

You said you had a resistor (R2? in your diagram- sort of) between Vout and ground (in the text). That should be between ground and control. It pulls the control pin low when the button is off. It's a "pull-down" resistor in that it pulls the pin to ground so it doesn't float. Your diagram shows it properly (R2 between 3 & 4). So check where you have it, I don't know which way you wired it (text or diagram).

R1 is an issue per your diagram. It's limiting current through the atty. The atty ground side should not go through that resistor, just the LED ground. In other words the R1 resistor should limit current through the LED, but should not be inline with the atty.

You don't need the cap for the atty side either, IMHO.

Hang in there! Those 4 pin regs are nice... voltage regulation and MOSFET function in one package. Switching is better than linear, but I've only used the linear so far. Still, it works great once you get it debugged.

Good Luck!

 

[Mark Linehan]

Sorry, I meant it was a 7805 style reg, I can barely read the numbers on this one I have had it a while. I do believe it is a 78R05. The pull down resistor is in deed between 3 and 4, and I had a second resistor in line with my LED to protect the LED. I kind of see what you are saying with the R1 stealing voltage from my atomizer, but I have to have the LED coming off of pin 2 to light it up, won't it pop without the R1?? ..or is the R2 somehow going to protect the LED???

I still can't figure out why my LED never turns off once the master switch is on. Whether I am firing the ATTY or not. I haven't measured the V across the atty yet either, but I can tell you the sucker is definitely getting plenty of power when I hit the fire switch because the atomizer starts spitting out plenty of vapor and I can hear the atty quite well so I don't know how much my LED/R1 are dropping me by, but it can't be too much, right?

 

[Mark Linehan]

@ Mark
I don't think you have a drawing for a 7805.
A 7805 has 3 pins
1: v in
2: Ground
3: regulated v out

(Edited to remove WAG)

If it is one of the 4 pin regs from MadVapes here is his drawing

My circuit is wired matching your schematic. I believe my pin outs are fine as it is operating properly except for the LED staying on always.

 

[Gummy Bear]

If I read your drawing correctly, r1 is in line between pin 3 and the atty, not in line with the led,
Quick test, jump around r1 and the atty -.

 

[AttyPops]

...... I kind of see what you are saying with the R1 stealing voltage from my atomizer, but I have to have the LED coming off of pin 2 to light it up, won't it pop without the R1?? ..or is the R2 somehow going to protect the LED???........

I wasn't worried about LED/R1 stealing voltage. The resistor, R1, is for the LED but not the atty as in your diagram. If you have the atty wired as in the other diagram (that gummy posted) then it's no problem. Yours shows it inline with the atty too, thus limiting current to the atty (making the atty a 473 ohm atty)..... I didn't say eliminate R1 from the LED.......just the atty. If it is sizzling, your diagram is simply drawn incorrectly compared to what you actually did.

The "always on" issue is confusing... we are lacking info. What is the voltage on pin #4 without the fire switch pressed? Also look for shorts... either to the Vout pin, or to the control pin.

 

[Gummy Bear]

I think we are trying to say to wire the led/ atty off of pin 3 like this.

 

[AttyPops]

Yes. Good work gummy. But he already did, or he wouldn't get sizzle. lol. The real question is "Why is it always-on?" Short or mis-wired?

EDIT: Also, check the specs on the regulator, but isn't R2 usually a K-ohm level (like 47K ohm) normally? I think there's some postings about that somewhere............

 

[kjj]

On your schematic, R1 should be on the same horizontal line as the LED, not on the vertical. If the thing produces vapor, I'm guessing that your schematic is wrong, not the device. If it was really in the place shown in the diagram, your coil would be working with 0.05 watts, and I don't think it would even get warm.

If you turn off the master power switch, does the LED go out right away, or does it linger? Does the LED go out when you press fire?

 

[AttyPops]

lol. Is there an echo in here?

 

[kjj]

Yeah, I even had paint open too. But I'm lousy with it, so it was getting less and less clear, thus I figured I'd try words again.

Something is wrong. You need to check, double check, and then triple check your device. It does not match either the diagram. If it were built according to your drawing, it wouldn't vape at all, and if built according to Gummy's modified drawing, the LED would go out within a couple of microseconds, even with very unlikely values for R₁ and R_atty.

The suspects, roughly in order of increasing probability:

1) You have a magic capacitor with an actual capitance 1*10^9 greater than the size and markings would suggest.
2) You have magic dirt coating the threads of your atomizer causing the resistance to be very, very high when the applied voltage is < 4v, and very, very low when the voltage is > 4v.
3) One of your wires is actually several miles long, tightly coiled, leading to higher than expected inductance.
4) Your LED and resistor are actually connected to pin 1 (and thus the battery) instead of pin 2.

 

[Mark Linehan]

Okay, so at least we know I am wired correctly (I think) and the schematic is wrong. The R1 is in line with the LED and I just didn't realize turning the corner with the component in the drawing changed the physical layout. I'm rusty with my schematic drawings still I guess. It is definitely wired properly on the 5x7 pcb though. Oh and both resistors are 470 for sure. I yanked the cap and it made no difference.

What makes me pause is the suggestion of the LED being on pin 1 instead of 2. I know it was not my intention, but perhaps there is some solder gone traveling. I tried to make things as compact as possible on this one, just for the hell of it. I eventually want to get all of this into a single AA box with a 3mm mister bottle juice feeder. So, I think I am going to have to desolder everything and make sure everything is clean and properly soldered again. Although, I think if I shorted 1 to 2 with solder there would be more problems showing up than just a steady LED.

Oh and the LED goes right on and goes right off. It stays on whether I hit fire or not. I would not be surprised by it if it went off when I hit the fire. That would at least give me a direction to go looking in. I can not remember why right now, but for some reason I was expecting it to shut off when I hit the fire switch at first. I do not remember a lot from my electronics classes almost 30 years ago but for some reason I thought the led turning off instead of on with the fire switch would have at least made sense somehow.

BUT.. We do know the following may be true..

1. My components are from Oz
2. I am a dirty old man
3. I have serious depth perception problems when it comes to wire length
4. I have trouble with sequences ranging from 1 through 4

..and my schematic skills suck..

 

[Gummy Bear]

An actual part # may be in order at this point. (and a Pic. )