Showing posts with label code. Show all posts
Showing posts with label code. Show all posts

Wednesday, June 12, 2013

Resistor Colour code convertor

This page tells you how to download and use the colour code convertor program
Click to Download
Internet Explorer will respond with a dialog box. You can decide whether to save the program to disc and run it later, or to open it straight away. Either way, there may be a further dialog box, giving dire warnings about downloading software from the internet. (DOCTRONICS knows of no problems with the program, but no guarantee is implied.)
The colour code convertor can be copied and distributed freely, but remains copyright ©. Distribution for profit seems unlikely, but is expressly forbidden.
The program was written using Borland Delphi 2.0.

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How to use the program

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1. Finding the resistor value corresponding to the colour code:
Hold your resistor with the tolerance band (usually gold) at the right hand end:



Within the colour convertor program, click on the FIRST DIGIT drop down arrow to see the choice of colours:

Notice that black is not available as a choice for the first digit colour.
Click on green. The focus moves automatically to the drop down list for the SECOND DIGIT, where you select blue in exactly the same way:

The focus moves again, this time to the MULTIPLIER drop down list where you select brown. As soon as you click the brown, the focus moves to the convert button, and the resistor value, 560 ohm, appears immediately in the result box.
When you select resistor colours in this way, the result appears automatically, without clicking the convert button. However, if you change only the first or second digit colour, without changing the multiplier colour, you will need to click convert to initiate the conversion process.
Note the effect of clicking on the ohm, k and M radio buttons. The colour code for 560 k is given, but 560 Mis outside the normal range of resistor values and generates an error message.

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2. Finding the colour code corresponding to a particular resistor value:
Suppose you want to find the colour code for a 390ohm resistor. The program allows you to do this in two ways. Clicking on the drop down arrow next to the result box gives a list of E12/E24 values from which you can select by scrolling through:
Once you have selected 390 from the list, click on the ohm radio button:
As soon as you click to select ohms, the display changes to show the correct colour code, in this case:

As an alternative, you can enter a number directly in the result box. Numbers with two significant digits are allowed, that is, 1.2, 12, 120, but not 121 or 473. If you want to know the code for 1 200 ohms, enter 1.2 and click k. Incorrect entries, or numbers which do not correspond to E12/E24 values generate appropriate error messages.

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3. Tolerance.
Tolerance refers to the percentage accuracy of the resistor value. Most resistors have a gold coloured tolerance band, indicating an accuracy of ±5%, but other colours are possible and can be selected from the drop down list.

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4. E12/E24 values.
Resistors are manufactured in values which correspond to the E12 and E24 scales. Details are given in the Resistors Chapter. The program indicates whether a particular value is included in both scales, or is an E24 value only.

Back to Resistors

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Tuesday, April 9, 2013

Low Cost Digital Code Lock

Many digital code lock circuits have been published in this magazine. In those circuits a set of switches (conforming to code) are pressed one by one within the specified time to open the lock. In some other circuits, custom-built ICs are used and positive and negative logic pulses are keyed in sequence as per the code by two switches to open the lock.

Digital Code Lock Circuit diagram :

Simple Low-Cost Digital Code Lock-Circuit Diagram

A low-cost digital code lock circuit is presented in this article. Here the keying-in code is rather unique. Six switches are to be pressed to open the lock, but only two switches at a time. Thus a total of three sets of switches have to be pressed in a particular sequence. (Of these three sets, one set is repeated.) The salient features of this circuit are:
1. Use of 16 switches, which suggests that there is a microprocessor in-side.
2. Elimination of power amplifier transistor to energise the relay.
3. Low cost and small PCB size.

An essential property of this electronic code lock is that it works in monostable mode, i.e. once triggered, the output becomes high and remains so for a period of time, governed by the timing components, before returing to the quiescent low state. In this circuit, timer IC 555 with 8 pins is used. The IC is inexpensive and easily available. Its pin 2 is the triggering input pin which, when held below 1/3 of the sup-ply voltage, drives the output to high state. The threshold pin 6, when held higher than 2/3 of the supply voltage, drives the output to low state. By applying a low-going pulse to the reset pin 4, the output at pin 3 can be brought to the quiescent low level. Thus the reset pin 4 should be held high for normal operation of the IC.

Three sets of switches SA-SC, S1-S8 and S3-S4 are pressed, in that order, to open the lock. On pressing the switches SA and SC simultaneously, capacitor C3 charges through the potential divider comprising resistors R3 and R4, and on releasing these two switches, capacitor C3 starts discharging through resistor R4. Capacitor C3 and resistor R4 are so selected that it takes about five seconds to fully discharge C3.

Depressing switches S1 and S8 in unison, within five seconds of releasing the switches SA and SC, pulls pin 2 to ground and IC 555 is triggered. The capacitor C1 starts charging through resistor R1. As a result, the output (pin 3) goes high for five seconds (i.e. the charging time T of the capacitor C1 to the threshold voltage, which is calculated by the relation T=1.1 R1 x C1  seconds). Within these five seconds, switches SA and SC are to be pressed momentarily once again, followed by the depression of last code-switch pair S3-S4.

These switches connect the relay to out-put pin 3 and the relay is energised. The contacts of the relay close and the solenoid pulls in the latch (forming part of a lock) and the lock opens. The remaining switches are connected between reset pin 4 and ground. If any one of these switches is pressed, the IC is re-set and the output goes to its quiescent low state. Possibilities of pressing these reset switches are more when a code breaker tries to open the lock.

LED D5 indicates the presence of power supply while resistor R5 is a cur-rent limiting resistor.
The given circuit can be recoded easily by rearranging connections to the switches as desired by the user.

Source : www.ecircuitslab.com
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