Basic 555 timer application help

[Mark]

Can someone point me in the right direction for a basic 555 timer
application tutorial or help me out here? I want to use a 555 to blink
a bank of LEDs at an exact frequency i.e. 5hz or 10hz.

 

[Terry Pinnell]

Can someone point me in the right direction for a basic 555 timer
application tutorial or help me out here? I want to use a 555 to blink
a bank of LEDs at an exact frequency i.e. 5hz or 10hz.

This illustrates the basics:
http://www.terrypin.dial.pipex.com/Images/555Astable+Driver.gif

For a bank of LEDs (up to the standard 555's absolute max rating of
200 mA, say 10 @ 20 mA or 20 @ 10 mA), you would change R1 and/or R2
and/or Ct to get your preferred flash rate (and duty cycle, which you
didn't mention).

For example, with R1 = 1k, R2 = 330k, and Ct = 0.47uF, you'd get a
flash rate of about 5 Hz, with close to a 50-50 duty cycle. You could
replace R2 with one fixed resistor of say 100k and a pot of 2M or 2M2,
to get a range of frequencies from about 15 Hz down to below 1 Hz.

 

[John Fields]

Can someone point me in the right direction for a basic 555 timer
application tutorial or help me out here? I want to use a 555 to blink
a bank of LEDs at an exact frequency i.e. 5hz or 10hz.

 

[Terry Pinnell]

Can someone point me in the right direction for a basic 555 timer
application tutorial or help me out here? I want to use a 555 to blink
a bank of LEDs at an exact frequency i.e. 5hz or 10hz.

Posted this earlier, but not confident my ISP news server (Demon) is
working properly, so excuse possible duplication:
-------

This illustrates the basics:
http://www.terrypin.dial.pipex.com/Images/555Astable+Driver.gif

For a bank of LEDs (up to the standard 555's absolute max rating of
200 mA, say 10 @ 20 mA or 20 @ 10 mA), you would change R1 and/or R2
and/or Ct to get your preferred flash rate (and duty cycle, which you
didn't mention).

For example, with R1 = 1k, R2 = 330k, and Ct = 0.47uF, you'd get a
flash rate of about 5 Hz, with close to a 50-50 duty cycle. You could
replace R2 with one fixed resistor of say 100k and a pot of 2M or 2M2,
to get a range of frequencies from about 15 Hz down to below 1 Hz.

 

[Mark]

Thanks a lot for the tip. Is there a way to caliberate the frequency
to say exaclty 10Hz without an oscilliscope?

 

[Terry Pinnell]

Thanks a lot for the tip. Is there a way to caliberate the frequency
to say exaclty 10Hz without an oscilliscope?

How accurate do you really want it? More or less accurate than your
spelling, for example? <g>

Seriously, what is the application that requires EXACTLY 10 Hz? If for
instance it's for some sort of clock, for which you require the sort
of precision associated with clocks, then forget about the 555 and
consider a high frequency crystal oscillator, divided down
appropriately.

 

[Robert C Monsen]

If you need more LEDs, you can use this circuit:

http://home.comcast.net/~rcmonsen/misc/20leds.GIF

It limits the current into the LEDs using whats called a 'current mirror'.

You can extend it to more LEDs, and adjust the brightness with R1. Note that
with the values in the circuit, the LED current will be about 35mA, which is
too high for normal LEDs. The circuit was designed with high current LEDs in
mind. Just adjust it using R1.

Regards,
Bob Monsen

 

[Mark]

Thanks for the diagram Terry. Since this is not going to be connected
to the mains power supply like in the diagram, can it simply be
directly connected in-line to the led bank power supply (battery?)
without a relay?

 

[Terry Pinnell]

Thanks for the diagram Terry. Since this is not going to be connected
to the mains power supply like in the diagram, can it simply be
directly connected in-line to the led bank power supply (battery?)
without a relay?

Yes. You can power the circuit from either a battery or from a
mains-to-DC supply (e.g. from a standard DC adapter). Use any
convenient voltage, such as 5V, 6V, 9V or 12V. Adjust the resistors in
series with your LEDs for suitable brightness. You didn't say how
large your 'bank' was, but don't forget the 200 mA 555 limit (100 mA
for CMOS type), or use transistor drivers as Robert illustrated.

 

[GPG]

Try this, any m/s ratio available at the expense of some accuarcy











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pin3 -|___|-----o---------- pin2,6
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GND


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+--|___|---<|----------o------ pin2,6
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pin3 ---+--|___|-->|-----------+
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