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Multiplexed LED Display

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Stony Brook...

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  1. Project Overview
  2. Laboratory Description
  3. Equipment used
  4. Circuit Design

Through a series of laboratory procedures, we have created a LED clock which is powered by a transformer whose voltage initially is a 120V rms. The purpose of the project is to understand how to use resistors, transformers, capacitors, and transistors to bring down the alternating current voltage of 120 V rms down to a safe direct current, and use that to power an LED clock.

[...] * Lab11.asm * * Created: 11/21/2017 10:58:48 AM * Author: Thomas & Abdul .def ticks = r16 .def secs = r17 .def mins = r18 .def hours = r19 main: //set up ports ldi r30, 0b00000011 Set up port C out ddrc,r20 ldi r20,0xff Set up port D out ddrd,r20 clr ticks clr secs clr mins clr hours ldi r16,0xfe out portb,r16 ldi r16,0b11000111 Set up port B out ddrb,r16 Increment ticks, secs, mins, and hours tick: sbis pinc,7 rjmp tick inc ticks cpi ticks brne displayTime clr ticks inc secs cpi secs brne displayTime clr secs inc mins cpi mins brne displayTime clr mins inc hours cpi hours brne displayTime clr hours displayTime: Seconds com secs out portd, secs com secs cbi portd Enable colon LEDs cbi portd cbi portb Enable seconds and colon LEDs rcall delay_21k sbi portb Minutes mov r20, mins rcall get_segs out portd, r21 cbi portb //enable digit 6 rcall delay_21k sbi portb //disable digit 6 out portd, r22 cbi portb //enable digit 7 rcall delay_21k sbi portb //disable digit 7 Hours mov r20, hours rcall get_segs out portd, r21 cbi portb //enable digit 1 rcall delay_21k sbi portb //disable digit 1 out portd, r22 cbi portb //enable digit 2 rcall delay_21k sbi portb //disable digit 2 Return to counting sbis pinc rjmp tick rjmp displayTime get_segs: clr r0 ;clear tens register div_m: cpi r20,10 ;bigger than ten? [...]

[...] We notice that the image of the oscilloscope is different from before (page 5). We now connect a piece of lead 1 inch long and connect it to the scope probes, this allows us insight into magnetic fields (Westerfeld Lab 7). We bring it close to the toroidal inductor and observe the magnetic field generated by the power supply (page 6). After all the experiments are done we install the microcontroller, ATtiny48, it is static sensitive to prevent damage we must be grounded whenever we handle it. [...]

[...] Circuit Design The first piece added to the circuit board is a fuse holder, this piece is there for safety reasons, it breaks the circuit in the event of excess current (Westerfeld Lab 6). We then install two diodes in location D1 and D4. The diodes prevent electrical current from flowing in a reverse direction, this assists us change the alternating current to direct current. The voltage will now only be above the 0 voltage line, in a graph. We then install a 100kohm resistor in R8, this resistor provides a small load to the circuit that makes the oscilloscope images clearer. We then install two more diodes at D2 and D3. [...]

[...] So by doing so our clock will not turn off every few seconds. Then, we install the USB connector J1. Allowing us to plug in our clock into a computer to program. We then install a 10 nF ceramic capacitor at C3, and a 22kohm resistor at R1. Then we install a SB560 Schottky diode D5, which helps with efficiency. Next we install a 470 ?F aluminum electrolytic capacitor in location C4. Then we install a 3.3 kohm resistor R9 on the circuit board. [...]

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