remote det. circuit problems

[jim2]

To all,

I am having troubles switching the transistor of the control circuit.Experimenting using a cell phone with wires leading from the vibrator. I built a controll circuit by using a NPN bc548 transistor to switch to a 9 volt load.I am getting a 1 volt input into the base of the transisitor which is not enough to switch to the load circuit.When I use a 1.5 volt AA battery the circuit works and the light lights up.Does any one know of a transistor that requires a lower voltage or maybe a stepup some how? Any ideas would be appreciated greatly. Thanks

[krickman]

I built almost the same thing as you are trying to build.
i used a optical relay that works in the area of 0,7-1,2 V (if i remember corectly) and that relay switches a mecanical relay that switches te power sorce. I built all this in a box with conektions so i could replace the cell phone with a timer and cahrge the built in led batery. works great.

[Tuatara]

Jim2 : a BC548 can be turned on with just 0.7V on the base. Without seeing your circuit it is very hard to identify your problem.

[Bert]

I for one would be interested in hearing the full application intended for the device, along with seeing a circuit diagram of what's to be built.

[Zeitgeist]

Show us your circuit, i can help.

[jim2]

thanks for all who posted.Sorry to wait so long to comment.I made another circuit with larger wire(to cut resistence) and another transistor and the controll circuit opened when I manually set the phone to vibrate,So that is OK.The new problem is that when I hook the vibrater leads to the circuit and someone calls me it rings instead of vibrating.I called myself and without the circuit the phone vibrates -no problem.

Any ideas what the problem could be???
I do not have a home computer and you can not download or upload at any of the cyber cafes around me (used mainly for e-mail and games ) so I can not put the circuit out but it is very simple to discribe.

I started with the transistor on a board.the base to (+ )from the phone.The Collector to the ground side of bulb and the postive side of bulb to the 9 v battery.The battery (- )and the Emitter and the phone( - ) are ground together on the board .Very simple but I know very little about electronics.

Bert, There is nothing being built but the circuit and the knowledge that I can do it, even if it is very simple the thrill is doing it and increasing my knowledge and confidence.Again Thanks to all.

[Zeitgeist]

OK try putting a resistor (Try Say 10K Ohm) between the base connection and the phone, and see if that will let the vibration work

[powdermunkey]

Zeitgeist's suggestion is a good one. You might also get a darlington type transistor and use 100 k ohms or so.

[SmallR2002]

Has anyone tried using a PC power pack? afterall the're pretty safe considdering that if they short they just turn off for a lill while. Just wondering because I have about five of them without the rest of the PC.

[jim2]

zeitgeist,

I tried putting a 1K resistor in the line before the phone and with a manual setting of the vibrator it vibrated but the load light did not go on ( I think the transistor did not switch).I will try a 10K and see what happens with a call.Thanks for the help.Will try today.

[Zeitgeist]

They are great things for general electronics experimentation use

If you need a power source for say Electrolysis they are good as the 5V rail usually carries a rating of at least 20 Amps.

[Zeitgeist]

They are good high quality high current power supplies for general electronics work, 5V @ up to 20A is good for electrolysis

[jim2]

HI,

I tried both a 10K and a 500 Ohm and the transistor is not switching.( it seems that with the large wire the resistence is low enough to let enough current to switch .I will try larger gauge wire from the vibrator to the base.(the 1st time I cut the vibrator off and used the leeds,this time I spliced into the vibrator wires to keep the load) both time the phone rings instead of vibrating.Any other ideas? This should be simple but I am doing something wrong

[grandyOse]

You are loading the vibrator circuit. Your transistor and vibrator are not compatable. You need a higher impedance load in parrallel with the vibrator and you can't get that by adding resistance, because it is lowering the input too much to operate your transistor. Try an optoisolator or darlington pair.

[Zeitgeist]

Ooh, my bad. I forgot i'd already posted that.

If the transistor route fails, try using an Optocoupler, yeah, a darlington (off the top of my head, a BD679 is a NPN darlington isn't it?) is the way to go though

[jim2]

I have been looking for the last 2 weeks to find a darlington transistor.None of the electronics suppliers have them.I even tried in another country but no one had them.I think I will try looking into the optical realm and see what comes up(maybe a LED and opticaltransistor).Any ideas ,thanks for all input.

Jim2

[T_Pyro]

Try asking for a BC517 darlington transistor. Optionally, you could simply make your own darlington pair from 2 npn transistors. www.fairchildsemi.com has a wide range of discrete components, and optoelectronics components to choose from.

[Zeitgeist]

BD681 is another from memory

[Jumala]

@jim2
at first forget the BC 548 transistor. If you have put 1 Volt to the base it may be already distroyed. A BC 548 needs a base current not higher than 1mA and can switch max. 200mA. This is ways to less.
A switching capability of 10-20A is useful.
You can build an own darlington transistor from BC 548 and 2N3055.
Put both collectors together and connect the emitter of the BC548 direct to the base of the 2N3055.
Then connect 220KOhm from base to minus. This is for savety because the darlington pair is sensitive to smallest currents.
Use 10-30 KOhm from the cellphone to the base.
The phone must have a continuous DC output and not a square wave signal to drive the vibrator.

You can also use a single power MOS transistor like 2SK3296 (N-channel up to 15V and 35A) This transistor can be found on K7S5Apro mainboards.
If you can get defect computer mainboards you find cheap power MOS in the switching power supply for the cpu, nearby the ring coils.

I have searched for a pdf datasheet at NEC´s homepage but I get only a blank page. So I don´t know to connect this transistor.

[jim2]

Jumala,

I got the parts today and started putting them on a board.I am a little confused because it is not like what I have done before so I have a question.

After connecting a 10 K in line from the cell to the base of BC548 and connecting the C of 548 to the C of 3055.connect the 548 E to the base of 3055 and a 220K from 3055 base to - ... As before does the 3055 Collector go to the - side of the light(load) and the 3055 Emitter to ground?

I just wanted to make sure before I did the last hookups.I have been learning a lot the last few months thanks to all the help and advise given.