Showing posts with label 555-Circuits-3. Show all posts
Showing posts with label 555-Circuits-3. Show all posts

## Wednesday, August 09, 2017

### +5 to -5 using a 555 Astable Multivibrator

This is a very simple -5V supply using one 555, useful for analog blocks using FET Opamps using low power. This circuit came up when i had to design limited by inventory. It worked well for its need. It converts Positive Five Volts to Negative Five Volts to create a dual supply.

This +5 to -5 using a 555 Astable Multivibrator.is not a high efficiency design, in fact it cannot take a heavy load. Circuits having some CMOS Opamps and a A/D convertor is ok. Even very small battery designs must avoid this circuit.

This suits well when you want to power an analog amp which has to measure voltages which swing on either sides of zero. It can be used in a LCD based portable measuring instrument running on a rechargeable 9V battery.

Powering a strain gauge amp may be one use, another may be like a RTD temperature meter for -50 to +150 deg C.

## Wednesday, February 18, 2015

### Astable Multivibrator with 555 Timer

The 555 Astable oscillator gives a square wave output at pin 3, The output drives two LEDs, LED1 lights up when pin 3 is low and LED2 when pin 3 is high.

The 555 can source (LED2) or Sink (LED1) upto 200mA. It can even drive a small motor or lamp with diodes added to protect from inductive kickback. Vary Ra, Rb and Ct and see the change of frequency, period and duty cycle.

These are the formulae used by 555 .

T1 = 0.693 (Ra + Rb) * Ct charge time of Ct

T2 = 0.693 (Rb * Ct) discharge time of Ct

T = T1 + T 2 total period in seconds

F = 1 / T = 1.44 / ((Ra + (2 * Rb)) * Ct) Frequency in Hertz

D = T 2 / T duty cycle, multiply by 100 to get %.

Ct in farads and Ra-Rb in ohms.

The max power dissipation of 555 is 700mW so overload of more than 200mA will damage the device, connecting the battery in the reverse or wrong polarity will also damage device, ensure also Ra and Rb do not go less than 2.2K (use 4.7K minimum) as it may damage the discharge transistor at pin 7. The supply voltage can go upto 18V. For CMOS 555 like 7555 see the datasheet they are different.

Interactive demo

This is a demo of the popular 555 timer. you can try out the project on this page by a javascript simulation.Press the Red button below to turn on the circuit press it again to turn off. The 555 can source (LED2) or Sink (LED1) upto 200mA.

It can even drive a small motor or lamp with diodes added to protect from inductive kickback.Vary Ra, Rb and Ct with the controls given and see the change of frequency, period and duty cycle.

This is a tutorial with calculator to help learn the application of 555 which is a very rare chip innovation. It is simple, versatile, flexible and programmable (by tweaking of pots).

Astable Multivibrato xml code

Screenshot of Astable 555 Timer Flasher

## Saturday, May 17, 2014

### 555 watchdog for uC and uP systems

When the microcontroller hangs due to a spike, EMI or RFI etc. the 7555 will reset the uC, if proper power supply design is done above circuit can also give a clean power on reset, the above circuit you should modify to suit your design.

80C39-8749 MCS-48 Examples and code

Better still use a uC with watchdog built in like some atmel chips, or use the watchdog chips from maxim which can also do RAM battery management.

The circuit was developed over a old TI application note, 7555 i think fairchild may be making it, 7555 is CMOS version of 555 timer, advantage of 7555 is that it can go to higher frequency, low power consumption, the disadvantage is its output drive mA is not as good as 555. now why i put it here was that you can see how charge and discharge paths are separated with diodes.

See Larger Circuit. 555 Watchdog
Edit the circuit eagle cad file del00013.zip,

## Circuits by Application

 Analog Circuits SCR and Triac Mains Power Digital Circuits Measureall DMM Mixed Circuits 555 Circuits Discrete Circuits Opamp Circuits Power Electronics uC and uP Instrumentation Circuits Process Control