REPAIRING AND NOT THROWING AWAY

Richtige Fernseher haben Röhren!

Richtige Fernseher haben Röhren!

In Brief: On this site you will find pictures and technical information about Service Modes, Circuit Diagrams, Firmware Update procedure, Disassemble procedure, Universal remote control set-up codes, Troubleshooting and more....

If you go into the profession, you will obtain or have access to a variety of tech tips databases HERE IT IS Master Electronics Repair !.

These are an excellent investment where the saying: 'time-is-money' rules. However, to learn, you need to develop a general troubleshooting approach - a logical, methodical, method of narrowing down the problem. A tech tip database might suggest: 'Replace C536' for a particular symptom. This is good advice for a specific problem on one model. However, what you really want to understand is why C536 was the cause and how to pinpoint the culprit in general even if you don't have a service manual or schematic and your tech tip database doesn't have an entry for your sick TV or VCR.

While schematics are nice, you won't always have them or be able to justify the purchase for a one-of repair. Therefore, in many cases, some reverse engineering will be necessary. The time will be well spent since even if you don't see another instance of the same model in your entire lifetime, you will have learned something in the process that can be applied to other equipment problems.
As always, when you get stuck, checking out a tech-tips database may quickly identify your problem and solution.In that case, you can greatly simplify your troubleshooting or at least confirm a diagnosis before ordering parts.

Happy repairing!
Today, the West is headed for the abyss. For the ultimate fate of our disposable society is for that society itself to be disposed of. And this will happen sooner, rather than later.

How to use the site:

- If you landed here via any Search Engine, you will get what you searched for and you can search more using the search this blog feature provided by Google. You can visit more posts scrolling the left blog archive of all posts of the month/year,
or you can click on the main photo-page to start from the main page. Doing so it starts from the most recent post to the older post simple clicking on the Older Post button on the bottom of each page after reading , post after post.

You can even visit all posts, time to time, when reaching the bottom end of each page and click on the Older Post button.

- If you arrived here at the main page via bookmark you can visit all the site scrolling the left blog archive of all posts of the month/year pointing were you want , or more simple You can even visit all blog posts, from newer to older, clicking at the end of each bottom page on the Older Post button.
So you can see all the blog/site content surfing all pages in it.

- The search this blog feature provided by Google is a real search engine. If you're pointing particular things it will search IT for you; or you can place a brand name in the search query at your choice and visit all results page by page. It's useful since the content of the site is very large.

Note that if you don't find what you searched for, try it after a period of time; the site is a never ending job !

..............The bitterness of poor quality is remembered long after the sweetness of todays funny gadgets low price has faded from memory........ . . . . . .....
Don't forget the past, the end of the world is upon us! Pretty soon it will all turn to dust!

©2010, 2011, 2012, 2013, 2014 Frank Sharp - You do not have permission to copy photos and words from this blog, and any content may be never used it for auctions or commercial purposes, however feel free to post anything you see here with a courtesy link back, btw a link to the original post here , is mandatory.
All posts are presented here for informative, historical and educative purposes as applicable within fair use. NOTHING HERE IS FOR SALE !

Wednesday, 27 February 2019

AUTO SHUT OFF TONE GENERATOR

Auto Shut Off Tone Generator


In this auto shut off tone generator project, once the switch to the 9V power supply is connected, the alarm will trigger at a frequency of approximately 1.27 kHz. It will remain ON for a duration of approximately 170 seconds or 2.8 minutes before it stopped.
This is a typical home burglar alarm system of which once the alarm is triggered ON, it will not be shut OFF until the duration of time set has elapsed. This project is useful when built as one can carry it along wherever one goes or placed it in a vehicle. In times of emergency, one can easily switched ON the switch and the loud speaker will emit a loud sound that will frighten the uninvited guest.



Schematic Diagram
The schematic of the tone generator is as shown below.

It is based on two 555 timer ICs or one single 556 timer IC(which contains two 555 timers). In this schematic, two 555 timers are used. U2 is configured as a timer in astable mode.
Once triggered, it will emit a frequency from its output at pin 3 that will drive a Q1 transistor. Q1 transistor will turn ON and OFF according to the frequency of the circuit. It will in turn used to drive a 8 ohm loud speaker to emit a loud audible sound.
The astable frequency of circuit U2 is given by the formula of 555 timer as shown below.
f = 1.44/[47K + 2(33K)][10nF]
= 1.27 kHz
The frequency of the sound can be adjusted by changing the values of R3= 47K, R4= 33K and capacitor C1=10nF. Change the values of these components and by using the formula for astable mode, the frequency of the sound can be obtained.
U1 circuit is used as a delay circuit which is configured as a monostable mode. It is a one shot multivibrator that will generate a pulse at its output at pin 3 which will disable the astable circuit U1. In this circuit, pin 2 of U1 will go to logic 0 when the power supply is connected via the capacitor E1 and hence circuit U2 is immediately triggered.
The pulse duration of the monostable circuit is given by the formula:
T = 1.1(330K)(470uF)
= 170 seconds
Once this timing is up, it the pulse output will disable the astable circuit of U2.

Parts List