Keyboard Encoder Operating Manual Ver.1.1 An ISO 9001 : 2000 company 94-101, Electronic Complex Pardesipura, Indore- 452010, India Tel : 91-731- 2570301/02, 4211100 Fax: 91-731- 2555643 e mail : info@scientech.bz Website : www.scientech.bz Toll free : 1800-103-5050
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Keyboard Encoder DB36 Table of Contents 1. Introduction 4 2. Theory 5 3. Experiment 9 To study Keyboard Encoder of 16 keys 4. Data Sheet 11 5. Warranty 13 6. List of Accessories 13 RoHS Compliance Scientech Products are RoHS Complied. RoHS Directive concerns with the restrictive use of Hazardous substances (Pb, Cd, Cr, Hg, Br compounds) in electric and electronic equipments. Scientech products are Lead Free and Environment Friendly. It is mandatory that service engineers use lead free solder wire and use the soldering irons upto (25 W) that reach a temperature of 450 C at the tip as the melting temperature of the unleaded solder is higher than the leaded solder. Scientech Technologies Pvt. Ltd. 3
Introduction DB36 is a compact, ready to use Keyboard Encoder experiment board. This experiment board has been designed to study encoding of 16 keys into binary logic and verify truth table. It can be used as stand alone unit with external power supply or can be used with Scientech Digital Lab ST2611 which has built in power supply, pulse generator, pulser switches, 8 bits data switches, logic probe, digital display, 8 bits LED display. List of boards : Model DB01 DB02 DB03 DB04 DB05 DB06 DB07 DB08 DB09 DB10 Name Logic Gates Universal Gate- NAND/NOR EX-OR Gate Implementation Demorgan's Theorem EX-OR Gate Application Code Conversion (Binary to Gray & Gray to Binary) Code Conversion (BCD to Excess-3 code) Binary Adder -Subtractor Encoder Decoder Multiplexer Demultiplexer DB11 Flip-Flops (R-S, D, J-K, T) DB12 DB13 DB16 DB15 DB17 DB21 DB22 DB27 DB28 DB29 DB31 DB32 DB35 Shift Register (4 bit SIPO) 4 Bit Synchronous Binary Counter Digital to Analog Converter (R-2R ladder) BCD to 7- Segment Decoder 3 Digit Event Counter Fiber Optic Digital Link Analog to digital converter (Counter Type) Digital to Analog Converter (R-2R ladder) Monostable Multivibrator CMOS and Crystal Oscillator Decoder/Demultiplexer Modulo-N programmable counter 4 BIT Shift Register and many more Scientech Technologies Pvt. Ltd. 4
Encoders : Theory An encoder is combinational circuit that performs the inverse operation of a decoder. if the a decoder's output code has fewer bits than the input code, the device is usually called an encoder. e.g. 2 n -to-n, priority encoders. The simplest encoder is a 2n-to-n binary encoder, where it has only one of 2n inputs = 1 and the output is the n-bit binary number corresponding to the active input. Octal-to-Binary Encoder : Fig. 1 Octal-to-Binary take 8 inputs and provides 3 outputs, thus doing opposite to 3-to-8 decoder. At any one time, only one input line has a value of 1. Below figure shows the truth table of a Octal-to-binary encoder. Truth Table : I0 I1 I2 I3 I4 I5 I6 I7 Y2 Y1 Y0 1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 1 0 0 1 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 1 1 0 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 1 0 0 1 0 1 0 0 0 0 0 0 1 0 1 1 0 0 0 0 0 0 0 0 1 1 1 1 Scientech Technologies Pvt. Ltd. 5
For an 8-to-3 binary encoder with inputs I0-I7 the logic expressions of the outputs Y0-Y2 are: Y0 = I1 + I3 + I5 + I7 Y1= I2 + I3 + I6 + I7 Y2 = I4 + I5 + I6 +I7 Based on above equations circuit can be drawn using OR gates. 16 to 4 Line Binary Encoder : Here is a 16 to 4 Line binary encoder which takes 16 inputs from 16 different keys and provides 4 outputs, thus doing opposite to 4-to-16 decoder. At any one time, only one input line has a value of 1. Below figure shows logic diagram and the truth table of a Decimal-to-binary encoder. D15 D14 D13 1 2 3 4 5 6 11 12 IC1 7430 8 IC5A 1 2 VSIN Z = D8+D9+D10+D11 +D12+D13+D14+D15 D12 D11 D10 D9 1 2 3 4 5 6 11 12 IC2 7430 8 U5B 3 4 VSIN Y = D4+D5+D6+D7 +D12+D13+D14+D15 D8 D7 D6 D5 1 2 3 4 5 6 11 12 IC3 7430 8 IC5C 5 6 VSIN X = D2+D3+D6+D7 +D10+D11+D14+D15 D4 D3 D2 D1 1 2 3 4 5 6 11 12 IC4 7430 8 IC5D 9 8 VSIN W = D1+D3+D5+D7 +D9+D11+D13+D15 D0 Fig. 2 Scientech Technologies Pvt. Ltd. 6
Truth Table : Scientech Technologies Pvt. Ltd. 7
From the above truth table, derived functions W, X, Y and Z are given below. W = D1 + D3 + D5 + D7 + D9 + D11 + D13 + D15 X = D2 + D3 + D6 + D7 +D10 +D11 + D14 +D15 Y = D4 + D5 + D6 + D7 + D12 +D13 + D14 +D15 Z = D8 + D9 + D10 + D11 + D12 + D13 + D14 + D15 Limitation : There is a limitation in this encoder circuit. If more then one inputs are active simultaneously, the output is unpredictable or rather it is not what expected it to be. This ambiguity is resolved if priority is established so that only one input is encoded, no matter how many inputs are active at given point of time. Priority encoder is the one which includes the priority function. The operation of the priority encoder is such that if two or more inputs are active at the same time, the input having the highest priority will take the precedence. Scientech Technologies Pvt. Ltd. 8
Experiment Objective : To study Keyboard Encoder of 16 keys. Apparatus required : 1. Digital board DB36. 2. DC Power Supply +5 V from external source or ST2611 Digital Lab. Logic diagram : Fig. 3 Scientech Technologies Pvt. Ltd. 9
Procedure : 1. Connect +5 V and ground to their indicated position on DB35 experiment board from external DC power supply or from DC power block of Digital Lab ST2611. 2. Switch ON the power supply. 3. Press keys one by one from 0 to 15 on 4 4 Keypad. 4. Observe output on LED display and note down output code for each key pressed. Observation Table : Key Output Code Scientech Technologies Pvt. Ltd. 10
Data Sheet Scientech Technologies Pvt. Ltd. 11
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Warranty 1. We guarantee the product against all manufacturing defects for 24 months from the date of sale by us or through our dealers. Consumables like dry cell etc. are not covered under warranty. 2. The guarantee will become void, if a) The product is not operated as per the instruction given in the operating manual. b) The agreed payment terms and other conditions of sale are not followed. c) The customer resells the instrument to another party. d) Any attempt is made to service and modify the instrument. 3. The non-working of the product is to be communicated to us immediately giving full details of the complaints and defects noticed specifically mentioning the type, serial number of the product and date of purchase etc. 4. The repair work will be carried out, provided the product is dispatched securely packed and insured. The transportation charges shall be borne by the customer. For any Technical Problem Please Contact us at service@scientech.bz List of Accessories 1. 2mm Patch Cord (Red) 16...1 Nos. 2. 2mm Patch Cord (Black) 16...1 Nos. 3. e-manual...1 No. Scientech Technologies Pvt. Ltd. 13