Retro RTC

April 5, 2010 4 comments

5th of April’10

<1130> Got up after a long sleep.

<1200 – 1300> WTH was I doing then? Probably taking some pills for having a good memory huh!

<1330> Had lunch.

<1600> Came back to room.

<1630> A KNOCK at my door.

A friend of mine was asking for some assistance in his mini project. I thought it would be fun and started discussing about it. It’s a retro RTC (Real Time Clock). The fact that I call this a retro is that he didn’t want to use any RTC chip and he brought an AT89C2051 microcontroller for this 24 hour clock project.

<1700> Project started.

It has a timer facility as well. The relay in the above picture is to drive a load connected to AC mains. Read more…


Home Automation through Cellphone Keying (H.A.C.K)

February 23, 2010 15 comments

I always wanted to control my lights and other appliances in my room remotely while I’m somewhere else. Many a times I forget to switch off the fan or AC in my room and then I have to go back and switch it off. I always wondered how cool it would be if I could control my appliances through something like my cellphone (which I never forget to take). Well now I can see that dream right in front of me. Yes, its yet another hobby project by Kaushani and me. Its the ‘Home Automation through Cellphone Keying(H.A.C.K)’ .

Fig.1 H.A.C.K’s Main Circuit

For those who are not aware of, for every key press on a standard telephone keypad an audible ‘beep’ is generated. It actually is a signal which is a combination of two distinct frequencies i.e. every key is uniquely defined by the combination of two distinct frequencies. Many (multiple) frequencies are used in which combination of any two defines a key on your keypad hence the name Dual Tone Multiple Frequencies (DTMF)’

Fig.2  DTMF  Frequency Combinations

H.A.C.K uses a Full DTMF receiver CM8870 from CMD which gives the binary output of the key being pressed. For more details refer the datasheet.

Fig 3 DTMF Receiver Circuit

The DTMF receiver circuit is interfaced with an ATmega16 MCU which is used to drive the external appliances ON or  OFF. For demonstration purpose I’ve used 3 leds to be my external appliances. I’ve also used my old NOKIA 2300 in the automatic answer mode and the earphone is used to give input to the DTMF receiver circuit.


  • Call the control phone from any other phone from anywhere in the world.
  • The control phone being in the automatic answering mode picks up your call.
  • Press the correct password to have access.
  • If the password is correct a buzzer will ring which you can hear through your phone   otherwise you can’t control the appliances.
  • Press Keys on your phone to control your appliances.
  • I’ve used the keys 1 to 7 to control the LEDS  but the other keys 8,*,0,# can also be included.
  • I’ve not used any password in the demonstration.

Feel free to post your queries and feedback in the comment section below.


Twimer – schedule your tweets

August 24, 2009 Leave a comment

This is a script that lets you to either ‘send your tweets at a sheduled time when you are not with your phone or computer ‘ or  ‘send a direct message as a reminder at your set time’. These features are already there in the web like twitter-timer and in futuretweets . However the script combines both in it. As per the present it has only these features but I’m trying to aggregate some more cool features in it. Kindly bear with these features till then. The present version has a maximun time of waiting of 24 hours ( made intentionally).You can add for particular dates and months as per your wish.

To run the script you’ll need python-twitter API. You can download it from here. Follow the installation steps.

You need to enter your username and password in some parts of the script.

api=twitter.Api(username='<username>',password='<password>') # enter ur usesname & password within qoutes

status = api.PostUpdate(tweet,'<username>')     # enter your username

directMesg= api.PostDirectMessage('<username>',dmesg) # enter your username


Note: when you are prompted with “Enter time(hh:mm): ”  it will take input in 24 hours format with hours and minute separated by ‘:’

eg.  20:15 for 8:15 pm

Categories: Codes Tags:

wep v9.04 : ‘Duplex Intercom’

April 9, 2009 Leave a comment

Its another technical weekend for Kaushani and me. After burning our grey cells in debugging the decade counter 7-segment display circuits of the first years in ‘Innovent’ ( organised by IEENC Manipal,MIT) we decided to come up with a new weekend project (Wep) and this time its a ‘DUPLEX INTERCOM . With a 6-12 Volts power supply its a very simple DIY hobby circuit using TDA7052 Audio power amplifier (manufactured by Philips) which gave us a gain of about 40db.

The very interesting part of this circuit is it uses very simple technique to minimise the ‘Larsen Effect’ which i’ll explain in a bit. First of all, there has to be (yes, you guessed it right!) two sets . I’ll call it SetA and SetB to make things clearer. Now whatever I speak in the mic in SetA should not get amplified in the speaker of the same set and similarly the speaker’s output(voice from SetB) shouldn’t be fed into the mic again.This audio feedback is what we call as the Larsen Effect and it becomes a very vital role to minimise this whenever you deal with audio frequencies .You must have felt  the Audio feedback many times -a high-pitched squealing noise during musical performances; that’s why we use monitors to avoid such effect. Now in this circuit the audio input signal is first amplified by a BC547 transistor and an intermediate output(before feeding into the power amplifier) is taken from collector as well as emitter of the transistor.As we know the output is in-phase and out-of-phase to the i/p signal in emitter and collector respectively, therefore by using a 22k Timpot we can minimise the input from the mic.The cable (o/p) from SetB  is fed at the collector of the transistor at SetA which we can hear in the speaker.

Can you see the switch (red colour) up there ? Well if you close this ,there won’t be any signal transmission but signal reception is independent of the switch.As we can’t get any log potentiometer in UDUPI, we managed with a simple 22k pot and it worked fine (of course not amplified as the way it should).We worked  using 9 Volts and the Duplex Intercom is running absolutely great!

For any queries and suggestions about the circuit, comments are always welcomed or mail us at




Wep v9.03: Audio Splitter for laptops

March 21, 2009 9 comments

Its yet another tech weekend for me and Kaushani. This time we have come up with a hobby circuit called the “Audio splitter” specially meant for laptops as we’ve taken the power supply from USB. Its implemented using TDA2822M Dual OPAMP IC with internal feedback which gives a gain of 89 (39db).

It has separate volume knobs for each headphone(o/p) as you can see in the photo below,works on a 10mA current.Its based on a prototype designed by Vasuki Prasad,an ex MIT,Manipal student.

Main features:

1. Power supply from USB (5 Volts)

2. 39db gain and low noise (A bit of hiss sound when fully amplified)

3.Separate volume knobs to control volume of your choice on each o/p.

4.Low cost (complete prototype @Rs 190)


(i) Wep stands for Weekend Project

(ii) Version format :Year.Month

Categories: Electronics, Projects

Zehen:Live in Revels’09

March 8, 2009 Leave a comment

Zehen’s performance in Revels’09…

Categories: All Misc Tags: ,

Evergreen retouched!

March 7, 2009 2 comments

Evergreen retouched!

Originally uploaded by wordiac

Ever Green rocked MIT with Deep Purple’s Perfect Stranger in Revels ’09. While the crowd was ponderously waiting for the problem with the equipments to be laundered,they came like a fire and swept the air around to a cyclone of thrills. Heretic was supposed to come but they didn’t turn up due to some circumstances. However, Ever Green expunged all the depression and kept the crowd alive. According to organizers, Opeth will be a wonderland for the next Revels.If it goes fine it will be awesome.So to all the music fans listen to Evergreen’s latest hit “Altar of Dreams” .

Categories: All Misc