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Showing posts with label digital. Show all posts

Showing posts with label digital. Show all posts

Two button Digital Lock

Posted by Unknown Tuesday, December 24, 2013 0 comments

Now here’s a digital lock unlike any other, as it has only two buttons instead of the usual numeric keypad. The way it works is as simple as its keypad. Button S1 is used to enter the digits of the secret code in a pulsed fashion-i.e. the number of times you press the but-ton is determined by the digit to be entered. A dial telephone uses the same type of coding (now maybe there’s an idea?). Press four times for a 4, nine times for a 9, etc. Pressing button S2 indicates the end of a digit.

Two-button Digital Lock Project Image:

Two-button Digital Lock Project-Image

For example, to enter the code 4105, press S1 four times, then press S2, then S1 once, S2 once, then without pressing S1 at all, press S2 again, then finally S1 five times and S2 once to finish. If the code is correct, the green LED D1 lights for 2 seconds and the relay is energised for 2 seconds. If the code is wrong, the red LED D2 lights for 2 seconds, and the relay is not energised. To change the code, fit a jumper to J1 and enter the current code. When the green LED D1 has flashed twice, enter the new 4-digit code. D1 will flash three times and you will need to confirm the new code. If this confirmation is correct, D1 will flash four times. If the red LED D2 flashes four times, some-thing’s wrong and you’ll need to start all over again. To finish the operation, remove the jumper and turn the power off and on again the digital lock is now ready for use with the new code.

Two-button Digital Lock Circuit diagram :

Two-button Digital Lock Circuit-diagram

The software can be found on the webpage for the project [1]. Don’t forget to erase the microcontroller’s EEPROM memory before programming it, so you can be sure that the default code is 1234 and not some -thing unknown that was left behind in the EEPROM. A little exercise for our readers: convert this project into a single-button digital lock for example, by using a long press on S1 instead of pressing S2 to detect the end of a digit.

Author : Francis Perrenoud - Copyright : Elektor

Source : http://www.ecircuitslab.com/2012/02/two-button-digital-lock.html

PIC Digital Clock Timer

Posted by Unknown Tuesday, September 3, 2013 0 comments

his clock timer uses a PIC16F628 microcontroller to display 3 and 1/2 digit time and control an external load. The clock includes a calendar with leap year and optional daylight savings adjustments. The timer output can be set from 1 to 59 minutes and manually switched on and off. The clock also has a correction feature that allows an additional second to be added every so many hours to compensate for a slightly slow running oscillator. The oscillator uses a common 32.768 KHz watch crystal and the frequency can be adjusted slightly with the 24pF capacitor on the right side of the crystal.

There are 7 displays that advance each time the D switch is toggled. To make adjustments, set the RA5 switch to the "B" position and then toggle the E and F switches to advance the data in the hours or minutes digits. Then toggle the "D" switch to move to the next data. After the 7th display, it will go back to the top and display the current time. Or, just press the time switch C to get to the top at anytime. When done setting everything up, set the RA5 switch to the "A" position so the data cannot be accendentally changed. You can still view everything with the "D" advance key, but the E an F switches will just turn on or off the alarm at RB7. I use it with an external transistor to switch on and off a radio.

PIC Digital Clock Timer Circuit Diagram

The Daylight savings setting (in the 6th display in the minutes digits) is used to enable daylight savings time adjustments, one hour ahead on the 2nd sunday in March, and one hour behind on the first sunday in November. The entry will be either 0, 1, or 3.

0 = Daylight savings time disabled (default).
1 = Savings time enabled and current time is standard time.
3 = Savings time enabled and current time is daylight savings time.

The last 2 entries on the list (Year and Correction) is for the current year (1 to 4) (4 = Leapyear) so todays setting (2006) will be 2 since leapyear will be on year 4 which is 2 years from now. The correction setting will add a second every so many hours for fine adjustment to the oscillator frequency. My setting is 18 which adds a second every 18 hours. Its pretty accurate and only loses 3 seconds a month. You probably want to run it for a couple weeks to figure out what correction is needed for the crystal you have.

Switch functions:

RA0         (C switch)         = Display Time
RA1         (D switch)         = Advance to next data (alarm, calendar, etc)
RA2, RA3    (E and F switch)   = Advance hours and minutes (in setup mode).
RA2, RA3    (E and F switch)   = Toggle alarm output on/off (in run mode)
RA5 in the B position (open) = Setup Mode

Download asm file

Digital Bike Tachometer SP

Posted by Unknown Saturday, April 13, 2013 0 comments

This digital SP tachometer for bikes uses 2 reed switches to urge the speed data of the bicycle. The reed switches are put in close to the rim of the wheel where permanent magnets pass by. The permanent magnets are connected to the wheelspokes and activate the reed switches everytime they pass by it. The speed is digitally displayed.

The tachometer circuit works in step with this principle; the pulses created by the reed contacts are counted inside an explicit time interval. The ensuing count is then displayed and represents the speed of the bike. 2 4026 ICs are used to count the pulses, decode the counter and management 2 7-segment LED show. RS flip-flops U3 and U4 perform as anti-bounce.

Electronic bicycle SP tachometer circuit diagram

The pulses arrive at the counter’s input through gate U7. The measuring amount is set by monostable multivibrator U5/U6 and might be adjusted through potentiometer P1 so the tacho are often calibrated. The circuit U1/U2 resets the counters.

Since batteries are used to power the circuit, its not sensible to support the continual show of speed data. This circuit isnt continuously active. The circuit is activated solely once a button is pressed. a minimum of 3 permanent magnets should be put in on the wheel. The circuit are often calibrated with the assistance of another pre-calibrated tachometer.

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