MicroScream: $5 Audible Lipo Alarm - Page 11 - RC Groups
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Dec 07, 2004, 09:57 PM
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Has anybody calculated the R values for a 4s1p battery?

I love these alarms and have them on all of my heli's, both 2s and 3s. Now I'm going to bump up to a 4s on my T-rex and I don't know if I can live without this alarm.


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Jan 07, 2005, 01:53 AM
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I take it nobody is making these anymore? Seems to me that a new company should be able to make these if the like90 won't do it. Is there a legal issue?

Anyone care to sell a couple "out of your garage"?
Jan 07, 2005, 02:37 AM
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can LED and Piezo be put in parallel

could I put an LED in parallel to the piezo so that it would be
activated at the same time. My hearing is not so great. It would be
good to have the added advantage of a pulsing White LED that needs
3.6 volts to start its oscillation. Would appreciate any comments on
how it could be added. Much thanks for your work here.
Crazy Ted -- a battery junkie

UPDATE: sorry to bother you, I just now read pages 7-9 and see the diagrams for pulsing LEDs. I need these for DLG which can go up so high I would not hear the piezo go off. Much thanks, again
Last edited by tjcooper; Jan 07, 2005 at 02:44 AM.
Jan 07, 2005, 03:08 AM
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I've gone thru the entire thread and saw that some have the buzzers always on.

Is this because the typical turn-on voltage of the 2n7000 is 2.1V and the voltage accross the TL431 is always maintained at 2.5V when pack voltage is always greater that 3.0V per cell?

Does it mean I have to select a 2n7000 by trial and error hoping that the turn-on voltage should be greater than 2.5 volts?

Please pardon if I don't make sense as I have very limited electronics knowledge.
Jan 07, 2005, 07:51 AM
Trying to defy gravity...
jimsky's Avatar
I don't know if it was ever actually determined just what the root cause of the problem that caused the alarms to be "always on" for the few builders that had this issue. So at this point it's just speculation.

Several things could cause this issue like; improper fabrication, ESD damage to componets, shorting of parts and the gate threshold issue I discussed is post numbers 25 and 27.

As mentioned, there is a possibility that component tolerances can stack up against you...creating a threshold problem. Personally I haven't seen it, but it can occur looking at the specs.

My goal was a minimal weight and parts count design. I took a chance on this simple design. So far for me, (the guys at like90) and many others; the MicroScream as designed has worked "as is". That's not to say a problem can't occur, and I did detail the possibility back in those older posts.

For a cheap as the TL431 and the 2N7000 are, I elected if a problem with threshold voltage did happen; I'd just try some other components to see if the tolerance issue would go away. Adding more parts to the design to address this issue is most certainally way to fix the issue, I just haven't found the need to do this yet.

Jan 07, 2005, 03:21 PM
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thekingofmice's Avatar
Thanks, Jimski!!! This is a great design -it worked on the first attempt, and operates perfectly. I appreciate that members like you take the time to share stuff like this with the rest of us.

Props to Digikey, too...I got my order in less than 36 hours!!
Jan 07, 2005, 05:23 PM
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Originally Posted by clearconcepts
I take it nobody is making these anymore? Seems to me that a new company should be able to make these if the like90 won't do it. Is there a legal issue?

Anyone care to sell a couple "out of your garage"?

I actually just got my parts to build one for a 3s pack on my RC Car. I ordered my parts from Mouser, so I used some different part #'s, as well as a different (but similar) buzzer. I forgot to order one of the resistors though, so I am going to see if my local electronics store carriers the one I need. I guess that when I finish building it, I can weigh it and post some pictures.
Jan 08, 2005, 12:11 AM
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I actually would need a 3s and a 4s for my cars if anyone makes extras. Has there been any 4s versions that work?
Jan 08, 2005, 09:15 PM
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I just finished my alarm tonight. I am using a different buzzer, since I ordered my parts from Mouser instead of Digikey. I have tested it with a 6cell NiMh battery pack (7.2v), and it did buzz like it should. This alarm is pretty small, and weighs only about 1/2oz. I even put tons of hot glue over it to make sure that nothing would short out (because of the dead-bug construction). I even hot glued the wires to the buzzer! So it is heavier than it needs to be, but it is going into my RC car with a 3s Lipo pack. Here are some pics:
Last edited by TMetalMan; Feb 14, 2005 at 04:59 PM.
Jan 09, 2005, 06:12 PM
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ricky's Avatar
Hi Guys,
I also had 6 that would stay on all the time. I changed the 341 first and then
the 7000 and they came out OK came to the conclusion to always use the static
wire on your wrist, all working ok after the change of the transistors. Did not bother
to determine which one it was that was giving me the problems, old went into the
garbage. Not bad out of 25. Good Luck!
And, Thanks Jim for a good simple Screeeeeemer!
Feb 14, 2005, 04:25 PM
Registered User

I know nothing abt electronics but can follow instructions and want to try making one of these...I'm a little confused about adding a led...someone said a 3-15v led attached to the + and - of the piezo will work....do I just attach it to the two ends of the piezo?

Feb 14, 2005, 05:56 PM
That tree again!!!!
thanhTran's Avatar
You need to add a register in between one of the LED's pins and the piezo pin

Piezo (+) +-------|>|-----^^^-------+ Piezo (-)

The register value should be about 470 ohms.

Feb 16, 2005, 03:54 PM
Registered User
thanks man, it works except for the crappy led I got from radioshack

thanks for posting this jim
Feb 16, 2005, 04:47 PM
Suspended Account
Steve Guinn's Avatar
Now that is a very pretty dead bug.
Mine works great, but is not quite as aesthetically appealing.

What do you say we have a "Ugliest Bug" contest?
Mar 13, 2005, 03:17 PM
The idea is great, just what we have all been looking for.
One question. Can you suggest anything other than a
buzzer as a signal? I am thinking of LMR gliders thermalling
at height a long way down wind?

My own thoughts would run to some sort of transmitting
device. Any ideas?

P.S.If I have missed something please accept apolagies,
I did not realise there were 6 pages! I shall go back and
read them now.
Last edited by flight999; Mar 13, 2005 at 03:21 PM. Reason: Omission.

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