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Wednesday, January 22, 2020

Audio Visual User Interface with Ack

This circuit is an User Interface part of a Security Alertness Monitor that i designed decades ago.

555 Buzzer and Pushbutton User Interface

The circuits are here - Digital Circuits - Part 1 The RAM and RTC part is missing, i will add later. It is without uC or Software. Only CMOS Logic.
 
Every Hour "+V UR" Goes High for 120 Seconds. The Buzzer Sounds and a Red LED turns on. The Guard has to respond by Pushing the Switch. The Green Light Flashes and the external Flip-Flop logic brings "+V UR" Low, The Buzzer Sound Stops and Red Light Goes off..

If not pressed the Sound Stops after 120 Seconds and even the Red light goes off then. This records a Non-Alert Hour in the RAM for that Day. The Ram Stores 9 Days alertness status.

You could try porting this project into a 89C2051 for learning product and interface design.

Power Supply with Battery Backup

This is an incomplete version of the power supply used for the Alertness Monitor with hourly LED Display. This circuit used a Dual Color LED. Green meant Alert and Red meant No Alert or acknowledge press.

Power Supply with Battery Backup

I can write here only in "Electronic English". Focus on the tech not grimmer. It may be like Pascal with a touch of Acronyms, codes and circuit axioms.

The top part is a 5V regulator with 0.7 Diode boost, means 5.7 V DC. The battery was floating on this point above the zener Z4, that connection comes from outside. A protection fuse maybe needed in case Zener draws more current. The Zeners were test selected to get above 6V along with the diode.

Power Electronic Circuits - Basic Power Supply Designs

The second supply is to drive the LED array and Relay. This second battery supply was needed to prevent the RAM from losing data and also the CMOS logic getting reset, when the relay solenoid operates. Even when the Display Now switch is pushed, the current is large and the pulse could reset digital circuit.

High Energy Circuits - What is High Energy ?

The battery was used very less, it worked during the power failures for short duration between mains and generator switching. This circuit is not meant for in situations when battery drains are high.

Telephone status indicator with LED

This will monitor telephone status without loading the telephone line, this way if you have two phones in parallel you will know if one of them is busy. Connect the two ends of circuit in parallel to phone lines.

Telephone LED status indicator

D1 to D4 make a bridge so that LED's are powered in correct polarity. LED1 indicates line ok no broken line, LED3 can light only when a 12V Zener breaksdown, this shows if line is busy or free, so that you dont go online when someone is talking on the phone in another room. LED2 lights on an incoming call ringing signal.

Learn on Gadget Hacks and Making Things

This is a higher voltage at least in older exchanges, so the cap protects the LED, and LED Lights when a AC ringing signal occurs. D6 protects LED2 from reverse polarity.

Learning Science to Promote Scientific Thinking

Science is best learnt with practical lab work in tandem with theory. Theory becomes appetizing only with practical experiments. In fact theory should follow practical experiments.

Monday, November 11, 2019

Display On Timer with 555

This is related to the earlier post. This was done to save battery power. The output of some equipment may be in the form of LED Annunciators In the Security Guard Monitor, an Array of 24 LEDs would show the Status of alertness along with the day, this was scrollable.

Display On Timer with 555

When the "Display Now" is pressed it triggers the Monostable Multivibrator made of a 555. The output "EN" goes high for the time duration defined by C27 and R71.

The 555 output as you know can drive more than 200mA for quite some time without much heating up. Many LEDs can be driven with the current limit resistors. I used CMOS chips to drive the LEDs, this circuit was used for the Logic only.

Hobby Projects - LED Circuits and Small Test Tools.

This circuit was a part of the user interface like the previous one. You could use it for voltmeters or even backlight for LCD.

Example - When you press the switch the Time of a clock can be seen in darkness for a few seconds.

Drive SCR thyristor with 555

This circuit gives a burst of pulses to fire 2 SCRs, when pin 4 is taken to 12V the SCR is turned on, to use this circuit you need 12V short pulses phase shifted with respect to AC sine wave on bridge, like this you can control the bridge from near 0% to near 100% ON.

Drive or Fire Thyristors SCR with Pulses

Drive SCR thyristor with 555

Learn about Thyristors here Power Electronics

That way battery banks can be charged, electroplating can be done, current and voltage can be controlled with opamps, thyristors are very rugged compared to transistors and MOSFETS in that order.