RC transmitter alarm

[Oldtoad]

This is the first time I have ever used a forum for anything so please bear with me if I'm wrong. To give a little background I'm a long time model aircraft builder/flyer and I'm having difficulty at the moment as my hearing is failing and I find it impossible to hear the countdown timer on my transmitter this is a small sounder built in that you can set for any time duration this bleeps at 1 minute and then counts down the last 10 seconds. My question is can I make a vibration device to retro fit so I can feel the timer though the body of the transmitter similar to a mobile phone. Can it be simply connected to the buzzer output. Does anyone have any experience of such a device and how to make and fit please.

 

[gophert]

You could connect a small vibratory motor (cell phone vibrate) to the output of the countdown timer. You may need a small transistor to raise the drive current to a suitable level.

 

[audioguru]

I can hear my transmitter's timer beeping when I wear my hearing aids but when sleeping without them I can't hear my phone, CO or fire alarms.

 

[Oldtoad]

Thank you gophert that sounds very promising, how do I determine what value transistor to use, I'm sorry for what seems probably a silly question but I'm a retired mechanical engineer and not very knowledgeable with electronics. With regards to audio guru I tend not to wear my hearing aids whilst flying as mine tend to amplify the engine noise to the point it hurts but still cannot hear the timer.

 

[Reloadron]

The current draw of the motor will determine the transistor to drive it. Most small motors like this are about 3 - 5 volt and I am seeing about 80 mA current. A simple 2N3904 or 2N2222 will handle 200 and 800 mA respectively so either should work. What needs known is the motor and where you can easily get a signal to drive it. Per gophert it should be pretty simple to fabricate it.

A Google of "small vibratory motor (cell phone vibrate)" will bring up a few dozen hits.

Ron

 

[Oldtoad]

Thank you Ron I was thinking of taking the power from the timer itself ie the buzzer mounted in the transmitter, I will remove the back of the Tx tomorrow and see what the voltage is going to it and post it here for further advice. Thank you all for your help it looks like my little project has some promise.

 

[Reloadron]

OTAY, that will work.

Ron

 

[audioguru]

The "beep-beep" timer warning from my Spektrum RC transmitter has a beep duration too short to drive a vibrator motor. I would need to use a monostable timer to increase the beep durations. The vibrator motor will be driven from the DC output of the monostable timer.

Another possible complication: A monostable circuit has a DC input but the beeper in your transmitter might be a little speaker that is driven with AC.

 

[Oldtoad]

Ah that complicates things can I check the speaker voltage to see if its ac or dc with a multimeter. A big thank you for all your advice I really do appreciate it.

 

[gophert]

Yes, you can put your meter on DC voltage and check if it reads anything while the alarm goes off. If nothing, there should be a capacitor next to the speaker. Easier again at the capacitor (on the lead distal to the speaker).

 

[Oldtoad]

Thank you I will check tomorrow and post results.

 

[Oldtoad]

Sorry for taking my time had to attend a breakdown/repair on my car. Anyway I have taken the back off the transmitter and exposed the terminals to the sounder (see picture) I have removed this board and on the other side is a standard looking black circular sounder. Whats strange to me is the voltage across these terminals is the same as the battery voltage ie 10.5v but when I trigger the timer it seems to drop when it beeps its difficult to tell by how much as it is quite rapid. I was expecting to get 0v and and a voltage when it beeps any idea why this is.

 

[Oldtoad]

Any help out there would be very much appreciated.

 

[audioguru]

We do not know if the sounder is a speaker with a coil or of it is a piezo transducer that does not conduct DC and is fed an AC signal.

 

[Oldtoad]

I don't think it's ac as I tried ac setting on my multi meter and got no reading. But did as described on dc, if that's any help

 

[Oldtoad]

How can i tell if its a speaker or piezo transducer. Thank you for your help.

 

[audioguru]

A speaker with a coil conducts DC then both terminals will have the same DC voltage.
A piezo speaker does not conduct DC so its terminals might have different voltages and it is fed a few volts of AC to beep.
Maybe it is a piezo buzzer that has an oscillator inside that is powered from DC.

 

[Oldtoad]

Is there any way I can tell would there be any part numbers or I'd on it do you think.

 

[audioguru]

If there is a part number then only the manufacurer will know its details.
Most of us would connect an oscilloscope to it to show what drives it.

 

[Oldtoad]

I'd u could borrow one could you talk me through it how to test. Going to bed now as its 1am in the UK were I am. Will let you know tomorrow if I can get one. Thanks again.