Transforming 12v to 9v

[ericgibbs]

Thanks. And what about the rest of the circuit components? I guess I don't know why capacitors would be required for this. ?

hi,
Look at this pdf for low voltage drop regulators, covers most common regulated voltages.

 

[3lectrokid]

I guess I don't know why capacitors would be required for this. ?

you connect the capacitors to stop the regulator from internaly ossilating so it doesnt not produce as much heat. there are no other componects needed (only ones are diode, 0.33uf cap, 0.1uf cap and 7809 regulator). before you connect anything to the output of regulator get a multimeter and measure the voltage just to make sure you are getting 9 volts.

 

[Hero999]

If you can't get hold of the LM7909, go with the 7808 - it should be fine.

What sort of wall plug adaptor does it use?

If it isn't regulated then it should be fine off 12V, the problem is the voltage might be as high as 15V - measure the voltage from the AC adaptor.

 

[undergraduate]

Thanks guys. Dang you guys are good. Hero999, The plug is a 9v AC adapter and it connects to the camera by way of those small millimeter pin and barrel connections. So I know that the two wires going to the camera are different polarity's because of that. I snipped the wire from the actual adapter plug and now am left with the two bare wires and the pin connector. One has the white stripes running across the wire and the other is solid black. I got mixed answers about which one is the common and which one is the positive wire. What do you think?

 

[Torben]

Thanks guys. Dang you guys are good. Hero999, The plug is a 9v AC adapter and it connects to the camera by way of those small millimeter pin and barrel connections. So I know that the two wires going to the camera are different polarity's because of that. I snipped the wire from the actual adapter plug and now am left with the two bare wires and the pin connector. One has the white stripes running across the wire and the other is solid black. I got mixed answers about which one is the common and which one is the positive wire. What do you think?

My earlier reply was wrong--the one with the stripe is likely to be +V. The other one should be 0V. But check with a multimeter first.


Cheers,

Torben

 

[Reloadron]

Generally the white striped wire is positive. If you do not have a meter or other device and want to measure polarity of the wall wart try to find a potato. Slice a small potato in half and try to poke each wire from the supply into the potato close to each other but not touching. One wire will turn the potato blue around the connection on the potato and that is the positive.

Ron

 

[Hero999]

You really need to measure the voltage with a DVM, the potato idea is a good one but it won't give you the voltage.

 

[Reloadron]

You really need to measure the voltage with a DVM, the potato idea is a good one but it won't give you the voltage.

Absolutely, I agree. The original post had a focus on determining the polarity and thus in humor I suggested using a potato for want of a good meter. Try as I will I have never gotten a potato to indicate the actual voltage. Maybe I need a better potato?

On another note, depending on the device driven a DMM is important. Most wall wart devices just put out an unregulated DC level that will be proportional to the line input. I have a 12 Volt wall wart sitting here I use to drive a 7805 regulator circuit. The actual output is about 14.5 VDC with a line input of 120.4 VAC.

Again, the potato was suggested in humor but will work for determining polarity. Once polarity is established the potato can be made into French fries.

<EDIT> My bad as when I returned to the thread I looked at the top post on this page. That seemed to focus on polarity. </EDIT>

Ron

 

[undergraduate]

Thanks ReloadRon. That potato thing is actually a good idea. I appreciate it guys.

 

[audioguru]

The OP kept talking about an AC adapter, not an AC to DC adapter. It might have an AC output.

 

[Hero999]

Lol, I'm now thinking you were having me on about the potato but half of me is thinking that it'll work but only with copper wire. The anode might be stipped of some copper which might turn the potato blue.

I seriously wouldn't recommend eating the potato afterwards as eating too much copper is very bad for you and if the wire is lead plated it's even worse.

 

[Reloadron]

Lol, I'm now thinking you were having me on about the potato but half of me is thinking that it'll work but only with copper wire. The anode might be stipped of some copper which might turn the potato blue.

I seriously wouldn't recommend eating the potato afterwards as eating too much copper is very bad for you and if the wire is lead plated it's even worse.

I was serious about the potato, LOL. I did screw it up though, the color will be Green for positive and not blue. I think I was about 7 years old when I did that experiment and I'll turn 60 next Sunday so I figure even remembering it was an accomplishment. I think I used nails but hell, can't remember. Green and not blue but it does work. Maybe later today I'll try it. There is bound to be a potato around here.

Totally off topic but I also tried cooking a hot dog with 120 VAC passing through it. That experiment went well but don't touch the hot dog when it is plugged in. You place a non-galvanized nail in each end of the hot dog as close to the ends as possible and connect each nail to one side of the AC Line (120 VAC for me). The process starts slow but as the hot dog gets warm the current increases. Really have to be careful with that method because you have exposed lethal voltage. Makes a good hot dog and quick. There were no microwave ovens in the mid to late 50s.

Ron

 

[undergraduate]

relays

Hey guys, me again. I have a relay I'm working with on this circuit. It's a KS2E-M-DC12 mini-relay and I just wanted to know If I need to wire the relay itself to ground and if so, which pin would it be?

 

[Reloadron]

No there is no requirement to ground the relay if that is what you mean. The relay is a DPDT with 6 connectors for the contacts and two for the relay coil. You may want to add a diode across the coil leads Cathode to your positive terminal and Anode to your negative terminal to suppress the inductive kick when the relay field collapses.

Ron

 

[undergraduate]

Camera transmitter

Hi gentlemen. Sorry not to start a new thread but I figure since this is the same project I'm working on and you guys know what's going on I'd just finish up here. My question is about a camera I have that is transmitting video and audio at 2.4 GHz wirelessly by way of antennae. I want to increase the range or distance that the camera is transmitting and I know that I can do that by doubling the length of the antennae... am I right? I opened it up and starting from the top the antennae has a wire, or at least I think it's a wire, covered by the plastic sheath. That's about 3 inches long and then it connects to what looks like to be a thin copper cylinder about 2 inches long. From there it runs to the back of the circuit board by way of a thicker wire that looks like to be covered by a braided fiber. Any ideas as to what's going on here?

 

[Reloadron]

Actually you may have done better starting a new thread but as long as we are here...

Making the actual antenna longer really won''t help much if at all. Antenna length is a function of frequency and a short wire antenna for 2.4 GHz would be about 4.92" long give or take.

If the camera is fixed and the receiver fixed (location wise) I would consider placing a small more directional antenna on the receiver if practical. Now if that is possible then maybe we can come up with something.

Again I think you would fare better with a new thread.

As to a directional antenna I would start with a Google of "Cantenna". There are other designs but a cantenna isn't too bad.

Ron

 

[undergraduate]

you connect the capacitors to stop the regulator from internaly ossilating so it doesnt not produce as much heat. there are no other componects needed (only ones are diode, 0.33uf cap, 0.1uf cap and 7809 regulator). before you connect anything to the output of regulator get a multimeter and measure the voltage just to make sure you are getting 9 volts.

I know it's been a while electrokid but where would I connect the diode exactly? I'm using a relay that turns on and enables the 12V car battery wire going into the relay. And from the relay output I've connected the 7809 regulator.

 

[audioguru]

The relay coil is an inductor.
When current in an inductor is suddenly stopped the inductance causes the current to keep going. It has nowhere to go so it causes a voltage spike of a few hundred volts across the coil which will destroy the driver transistor.

When a diode is connected parallel with the coil but with reverse polarity then when the relay is turned on the diode does nothing but when the relay is turned off then the diode conducts and shorts the high voltage spike to the power supply which barely changes.

 

[undergraduate]

The relay coil is an inductor.
When current in an inductor is suddenly stopped the inductance causes the current to keep going. It has nowhere to go so it causes a voltage spike of a few hundred volts across the coil which will destroy the driver transistor.

When a diode is connected parallel with the coil but with reverse polarity then when the relay is turned on the diode does nothing but when the relay is turned off then the diode conducts and shorts the high voltage spike to the power supply which barely changes.

Awesome, thank you. You pros make it seem so easy.

 

[qc4000]

good place to be

It is nice to see you guys willing to hold hand of newbies - I'm one of them and you should be hearing from me soon too.

I know now I have come to the right place.

Cheers, over and out!