How to make a 9volt Battery to output only 5-6volts??? at DVinfo.net

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Old April 3rd, 2005, 10:13 PM   #1
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How to make a 9volt Battery to output only 5-6volts???

I have a pair of EARTEC TD-900's so that my Sound Mixer can privately communicate with the Boom Operator when shooting. I wired the Mixers TD-900 into the media cart and the incoming signal directly into a Aux Return on the Mixer, and then dedicated a channel routed to a Aux Send to talk back. The boom operator wears the TD-900 as normal...this setup is sweet and it allows the Boom Operator to mix in with the mixers main feed with volume control as needed, and the Boom operator can hear whatever line the mixer wants him to, and mix that with his own voice as well. All this in Full Duplex.

This works well so that wirelessly the mixer can quietly tell the boomer to "raise up, your boom is in the shot" or whatever else he needs to privately tell him without the sound dept. getting embarrassed and hearing aloud it from some mouthy P.A. sitting in Video Village or whatever. Much more professional.

Anyhow, the Mixers TD-900 is powered with a 5vdc wall-wart spliced into the battery compartment, so it never needs batteries.
The Boom Op's TD-900 is still using the 700mah/4.8v rechargable battery pack that it came with. <--- THIS IS A PROBLEM!!
This is the ONLY thing left in my kit that has to be "recharged". Everything else either takes AA or 9v batteries. A standard 9V battery will fit nicely in the battery compartment, howver....it's too much voltage. I've already tried it, and after researching, I found that it only works if I use it with a 1/2 dead 9V battery. A fresh new 9V battery is just too much voltage.

SO, THE QUESTION IS...is there something small...like a diode or resistor or something (i'm no electrical engineer, so forgive me), but is there something I can pick up from the local Radio Shack and place it in line on the ( + ) wire side between the TD-900 and the 9v battery that will reduce the voltage of a fresh new 9v battery down to around 5-6 volts??

A link or any help would be appreciated...

- ShannonRawls.com
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Old April 3rd, 2005, 10:20 PM   #2
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Eartec makes a 9v adapter for the 900 series. A standard 9v should last approx 7-8 hours.

http://www.bhphotovideo.com/bnh/cont...=306137&is=REG
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Old April 3rd, 2005, 10:36 PM   #3
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The easiest way to do what you want is to us a 7805 5V regulator. The only problem is that it will use power even when everything is off. If you are sure you only ever want to us 9V batteries, you could (depending on the wiring) put the regulator after the on/off switch.

That said the 9V adaptor at B&H doesn't look like it has any electronics at all - maybe the headset can handle 9V straight?
How game are ya?
Maybe the manufacture will help if you word the questions right?

Bear in mind I know nothing of the TD-900, or it's electronics.

Good luck.
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Old April 3rd, 2005, 10:40 PM   #4
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<<<-- Originally posted by Marty Wein : Eartec makes a 9v adapter for the 900 series. A standard 9v should last approx 7-8 hours.

http://www.bhphotovideo.com/bnh/cont...=306137&is=REG -->>>

NOPE...eartec doesn't support that anymore...I found that too. *smile*

They said that was for the OLD ORIGINAL td-900's...not the new updated ones, and that they wish B&H didn't sell that anymore, cause it wont work. *sad face*


ABOUT THAT REGULATOR....
I found it at Radio Shack... Looks small and promising.....
http://www.radioshack.com/product.as...ct_id=276-1770

It looks to have 3 prongs....what do I do? How do I wire/solder it?

- Shannon W. Rawls
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Old April 3rd, 2005, 10:49 PM   #5
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As Kyle stated the regulator circuit is the most efficient.You asked about diodes and in fact a diode drops the voltage by .6v, 7 of them in series would drop voltage 4.2vHowever if your not familiar with electronics you probably should refer to a tech
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Old April 3rd, 2005, 11:06 PM   #6
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http://www.national.com/ds/LM/LM341.pdf
IN +9V DC
GND -9V DC
OUT +5V DC
I would use diodes since they need less power.

As for the boom operator, a small monitor (on the boom) receiving pic from camera (wireless) will guide him instantly as where about his boom is (in or out the frame) Hope this helps.
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Old April 3rd, 2005, 11:20 PM   #7
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Kyle, Jack & Dan,

Hmmm, that 3-prong regulatror seems promising and easy to solder up. But as Kyle mentioned, because I have to solder the GND line from the battery to the regulator as well (middle prong), hen it seems it will simply drain the battery until it's dead because the regualtor is "always on".

Now, as Jack & Dan said....Diodes seem prmising as well. About 6-7 of them all soldered in-line together and placed in the ( + ) line between battery & TD-900 should work....correct? This way, it will not use any battery juice when the TD-900 is turned off.....i guess. I could wire em up, and then Fold & Band them together and set them to the side of the 9V battery in the case.

What do you think? If so.... which part number from Radio Shack. WHen i did a search on "DIODE" 21 results came back. lol

- ShannonRawls.com
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Old April 4th, 2005, 12:18 AM   #8
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it will simply drain the battery until it's dead because the regualtor is "always on">>
not if your on/off switch is first connected to battery and then to 7805. In other words you power it all up when you need it.
And if you do not know precise value (how many volts) or need variable output (like 5 or 6 or 7 and anything in between, get a 317 (ask for positive adjustable regulator) They have the schematics on the back of the package (from where to where to solder)
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Old April 4th, 2005, 02:09 AM   #9
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A few points:
Both diodes and regulator will waste energy as heat.

The diodes won't use any power when the system is off.
They will also drop 4.2V (or whatever) regardless of input voltage, so as the battery goes flat, the voltage will drop until the radio won't work anymore. The regulator will continue to work until the voltage drops to the threshold value so it may 'last' a bit longer.

The pinouts are, as Dan said, in, gnd, out (ie +9v, 0v common, out).

I wouldn't use the LM317 adjustable regulator as it needs two resistors to set the bias voltage and that would make it more bulky.

You could measure the current the radio draws when transmitting and you might even be able to cut off the heat sink lug to make it more compact.

For diodes you could just get a small (physically) power diode 1N4004, etc space might be a concern with this option.

Robustness would be a concern for all options, with you changing batteries all the time, solid component legs could break over time.

If there is sufficient room to mount the regulator inside the case, probably near the switch, I'd do that. Note that this will only work with 'proper' switches, not the hold-down-to-turn-on type buttons like on mobile phones.
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Old April 4th, 2005, 08:32 AM   #10
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Shannon,
I just got off the phone with Scott at Eartec (800-399-5994) and was advised that back a month ago they had some minor issues with the 9v adapter and that it has been solved.

The current 9v adapters WILL work with the TD-900 Series.
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Old April 4th, 2005, 09:10 AM   #11
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>>LM317 adjustable regulator as it needs two resistors to set the bias voltage and that would make it more bulky<<
I had a pot in mind (to tune up more out as the V on the battery drops)
If you need 6V why not use 4AAA (or AA) or better yet 5 X 1.2V NIMH rechargeable. They will last forever.....
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Old April 4th, 2005, 12:34 PM   #12
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<<<-- Originally posted by Dan Diaconu : >>LM317 adjustable regulator as it needs two resistors to set the bias voltage and that would make it more bulky<<
I had a pot in mind (to tune up more out as the V on the battery drops)
If you need 6V why not use 4AAA (or AA) or better yet 5 X 1.2V NIMH rechargeable. They will last forever..... -->>>

I agree with Dan.

This would be the way to go if you have the space.

You can get from a radio shack battery holders that fit 4 AAA batteries or 4 AA... The four batteries should be wired in SERIES to give you 6 volts.

- [1.5]+ -[1.5]+ -[1.5]+ -[1.5]+
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Old April 4th, 2005, 01:54 PM   #13
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better yet, get five mini NIMH/NiCd (5X1.2V=6) and you can recharge them (not to mention they will last forever....)
Cordless phone size (usually come in packs of 3= 3.6V)
or even photo batteries of 6V (Lithium)
*smile*
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Old April 4th, 2005, 08:14 PM   #14
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I would have gone for using two discreet resistors if there was a space constraint. In reality you would never change the voltage and a pot would just introduce the possiblility of going out of adjustment. You could buy a 5 volt regulator and be done with it.

4AAA's would be a great option (if they fit), but Shannon said he wants to use 9V or AA - I guess AA's won't fit either. If 4xAAs fit that would be perfect (provided the radio can handle an extra volt, which is highly likely).

As far as the NiMh/NiCd route, I thought Shannon was trying to get away from rechargables.

Cheers.
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Old April 5th, 2005, 01:19 AM   #15
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WOW, I come back and all this good info from great online friends...

ok.... in order of posts since my last statement.....

Dan, I can't wire the regulator to the power switch because...i just cant. it;s soldered to the board and I ain't about to get all into that mess!

Kyle, thanks...I think you just out the nails in the coffin for the diodes. if they subtrack 4.8 volts from whatever voltage i give it, then when the 9-volt reasches 7 (real) volts, it will only give the td-900 2.2 volts...and that ain't cutting it. SO a regulator is now back on my list, and I will probably just buy enough 9volts to last a whole day and keep the unit on all day...it;s better then rechardging for me, trust me. and thanks for that important notice. And what is a LM317?? I thought the Type: 7805 was the regulator I should use?

Marty, I will call Eric tomorrow!!!!! That;s the best news thus far. When I called them they said "Sorry, wont work" but know I have a new person to ask for and I will infact ask THEM to sell them to me to make sure I get the right stuff (i will report back)

Dan & John, I cant use 4-AA batteries cause they wont fit in the battery compartment. I mean they fit, but not with all the erxtra stuff I would have to add to make them fit (like springs, metal tabs, etc...) and a 4-aaa battery case SURELY wont fit. And I refuse to velcro some big ugly battery box on the outside of the TD-900 unit. *smile*

Dan, sounds good, but my whole point is to not have to recharge anymore. It recharges NOW, but it's too much to worry about in a faced paced film shoot or after an 18-hour day.

Kyle, Discreet resistors?? please explain? Radio Shack??

- ShannonRawls.com
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