555 timer IC toys for children with disabilities

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mark3 20 years ago

Hi, can any one help? I,m just teaching myself basic electronics and have built a hobby kit (9V) using a 555 timer to tigger a LED off/on over various lengths of time. Have run a lead from pin 3 of 555 timer IC to base of transistor (548) to trigger 9v electric motor without success,I have also tried using a 9v relay but again not enough power to drive electric motor. My aim is to set up various tigger switchers with timming cicuits to drive different toys and lights to help stimulate learning for a child with intellectual dissabilities. If any one could offer some advise and/or some easy to read circuit diagram's in this area it would be greatly appreciated.

Thankyou

Mark3

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Jason 20 years ago

Instead of using a 548 NPN device, perhaps you should try using a MOSFET. Bipolar transistors act as a "switch" for current input and the maximum output current of the 555 timer (~1mA) will limit the current that your 548 can draw from your battery. If you switch this to a (high-power?) FET, you will be able to set your own limits within your range by picking the right device. FETs work off of the voltage levels applied to the gate and you don't have to worry about current limitations of the 555 timer.

This, of course, is all assuming that you've hooked up everything correctly and it is a problem with the 548 transister's capabilities.

gl,

Jay

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Bob Monsen 20 years ago

If you have an extra NPN transistor, try this:

View circuit using 'courier' or other fixed space font:

9V -------------o---- MOTOR + terminal | - ^ | .---o---- MOTOR - terminal | | |/ | PIN3-[1k]--| | |> | | | | |/ '-| |>

| | GND--------------'

This is called a 'darlington' configuration, and it boosts the output with a wimpy input.

Also, use a 1uF and a 0.01uF cap across the Vcc and Vdd inputs of the

555, or the voltage drop when the battery turns on may retrigger the timer. Even better, use a separate battery, and connect the grounds.

The diode protects your transistors.

Regards, Bob Monsen Mathematics is nothing more, nothing less, than the exact part of our thinking. - Luitzen Brouwer

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PeteG 20 years ago

A 555 timer can source/sink ~200mA so not only could it drive a small relay directly it has no problem driving BC548 or a power darlington transistor. You should check the manufacturers data sheet for the actual 555 timer you are using. The CMOS versions of this chip have lower output ratings.

Here's a couple of links to show you the way, and if you Google for 555 timer circuits you'll find a shed load of info'

formatting link

Pete

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Stefaan Vanheesbeke 20 years ago

What do you mean with not enough power??

Is the battery going down, or is the driving system not ok?

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mark3 20 years ago

Hi jay Thankyou for your time and help

Kind regards Mark

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mark3 20 years ago

Hi jay Thankyou for your time and help

Kind regards Mark

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mark3 20 years ago

Hi Pete Thankyou for your time and help. The web sites are very useful !

Kind regards Mark

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mark3 20 years ago

Hi Pete Thankyou for your time and help. The web sites are very useful !

Kind regards Mark

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mark3 20 years ago

Hi Bob Thankyou for your time and help

Kind regards Mark

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555 timer IC toys for children with disabilities

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