f = 1.44/[C*(Ra+2Rb)]where
- Ra is between Vcc (Pin #8) and Pin #7 (Discharge)
- Rb is between Pin #7 (Discharge) and Pin #6 (Threshold)
- C is between Pin #6 (Threshold) and Ground (Pin #1)
ensure Pin #4 (Reset) and #8 (Vcc) are tied together, and Pin 5 (Control) needs a filter cap if the circuit has noise problems.
ALWAYS A L W A Y S ALWAYS! Start with the cap. Set it by pulse width. Use this table:
Cap(uFd) Pulse width(Seconds) -------------------------------- 10.0 90m - 1.2 1.0 9m - 120m 0.1 900u - 12m 0.01 90u - 1.2m 0.001 9u - 120u --------------------------------Select your cap, THEN select the resistors. If you want to make it easy, ASSuME the resistors are the same value, then you can use:
f = 0.48/R*C <==> R=0.48/f*CIf your resistor is abnormal in size, you have either chosen the wrong cap, or you are doing some kind of real odd freq.
Mark Willis says:
[The] original 555's which were sort of power hogs; Use a low-power CMOS version, and make sure you have that version's datasheet if you use one, if you go the 555 route. Also, [you] could drive a 555 at a higher frequency and divide it's frequency down by a proportional amount.Electrolytics have huge temperature coefficients, using one for timing a 555, you want something like a Mylar or other low-variance cap. Those gre REALLY pricey IIRC by the time you reach 100uF, so use smaller C, larger R, and watch the construction, leakage on those pins 6 and 7 will change your timing.
Roman Black says:
I've been playing with 555s since 10 years old. You can also use a single inverter from a logic chip to replace a 555 in 95% of circuits. For a 14pin chip you can get 6 oscillators vs 2 in a 556.{see: http://www.users.dircon.co.uk/~doctron/chuckles.htm look at the gated astable circuit}
Also:
See also:
Questions:
file: /Techref/logic/555s.htm, 4KB, , updated: 2011/5/3 05:43, local time: 2024/12/25 09:40,
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