AVT724 - Universal timer controlled by a button or touch sensor
Timer can work in two modes: typical Timer or Staircase switch. In the first mode, after pressing the button, the timer changes the state of its output for a certain time and then returns to the standby mode. In the stair switch mode, each pressing of the button changes the output state to the opposite. After the set time has elapsed, the state changes again.
• Status signaling by two-color LED.
• Touch button or push button control.
• 2 working modes: Timer or Staircase switch.
• Relay output.
• Power supply: 9-12V DC.
• PCB dimension: 39×53mm.
• Electronic Kit – soldering required.
The schematic diagram is shown in Figure 1. The US1 (4017) operates a counter to 2. Each time the S1 button is pressed, the pulse occurs on the CLK input. The state of the input is determined by the state of the input ENA (pin 13 U1). If the points X and Y are shorted, the input is permanently set to low and each pulse on the CLK input changes the counter state. The first pulse will result in a setting of the output Q1 and the red LED will be on. Next will set the output Q2 and reset the counter - logic “1” will occur at output Q0 and the green LED will light on. When the Y and Z points are shorted, the output Q1 is directly connected to the ENA input. In standby mode, when output Q0 is set and output Q1 and input ENA are reset, counter can count. After the first impulse on the CLK input, the Q1 output and the ENA input will be set, and this will block the counting ability – subsequent pulses at the CLK input will not cause any counter response.
Assembly and test
The assembly diagram is shown in Figure 2 in the user manual. The assembly must be carried out in accordance with generally accepted principles. Particular attention should be paid to the orientation of electrolytic capacitors, transistors and diodes. After checking the correct installation, power supply can be connected: 9V battery or (better) stabilized power supply (9-12V).
The mode of operation of the timer can be selected with two points X, Y, Z:
- X-Y shorted – intelligent timer with switch on / off.
- Y-Z shorted – a typical timer, which measures the time after pressing the button.
Timer operation can be arbitrarily adjusted by changing the values of resistance R3 and capacitance C3 in a very wide range. On the PCB there is space for optional mounting of additional C5 capacitor, and potentiometer PR1. At first, a resistor R3 = 1MΩ and a capacitor C3 = 10uF is proposed, which allows for a delay time of up to 10 seconds.
R1, R2: 10MΩ
C1, C2: 10nF C3: 10uF
LD1: LED diode R/G
US1: CMOS 4017 IC with 16-pin IC socket
JP1: Goldpin connector 1×3pin + jumper
X1, X2: 2-pin terminal block connector - 3pcs.