Humans are born of habits, they want more and more comfortable. In order to match their requirements various types of automatic control system has been developed. Now, again here we have come with very interesting projects called “Industrial Timer Circuit” with facilities like automation and switching, providing delay and have long range of control (100 m).
Simple timer circuit can be designed using 555 timer IC by configuring it into monostable mode. These types of circuits have various types of limitations like digital display, indication of system failure, remote (wireless operation), alarm etc. The above listed limitation can be overcome using the project “Industrial Timer Circuit”.
Before starting discussion on circuit description and working, here we have listed some features of Industrial Timer Circuit.
Features of Industrial Timer Circuit
- Initialization and switching process after desired or predefined time with delay facility.
- 1 to 60 seconds time can be set which can be extended by editing software code.
- On/Off time is programmable thus one can program time from 1 to 60 seconds.
- Facility like single or continuous mode is available.
- Wireless remote facility with range of 100m.
- For better user interface, a LCD with front-panel control is available.
- An emergency stops buttons in order to avoid any unusually operation in both control panel as well as in transmitter circuit.
Circuit Description of industrial timer circuit
The circuit of “Industrial Timer Circuit” is divided into two main section i.e. transmitter and control section. Here at first let’s discuss about transmitter section.
Transmitter Section: The circuit diagram of transmitter section is shown in figure 1. The entire circuit is built around encode IC HT12E (IC5) and 433 MHz radio frequency transmitter module with some other electronics components for working flawlessly. In order to set address ‘00h’ all the address pin of IC5 connected to ground as shown in circuit diagram. Data pin of RF transmitter is connected to Dout pin (pin 17) where 1 M resistor is connected to oscillator pin (pin 15 and 16) of IC5. Four push-to-on switches (switch SW10 to SW13) is connected to data input pin through diodes. The function of keys is listed in table 1. Where LED (LED3) is used to indicate whether the switch is pressed or not. Pin no 14 (TE) pin is connected directly to ground through switch SW14.
For less complexity, we further divided the control circuit into two main sections i.e. receiver section and control section.
Receiver Section: The circuit diagram of receiver section is shown in figure 2. It includes decoder IC HT12D (IC2), RF receiver module and 4-input NAND gate IC. Al the address pin of IC2 is connected to ground in order to set address ‘00h’ as in transmitter section. Data pin of IC2 is connected to microcontroller through a 4PDT switch SW8 and connected to input of 4-input AND gate IC (IC3) as shown in figure 2. The output of AND gate IC is connected to reset pin through ON/OFF switch SW9. LED2 is used to indicates the reception of data from transmitter. Two resistor R4 and R5 is connected between oscillator pin (pin 15 and pin 16). Here we had used series connector in order to get 51K-ohm resistor. The output pin of RF receiver RX1 (pin 2) is connected to DIN pin (pin 14) of IC2.
Control Section: The circuit diagram of control section is shown in figure 3. In includes a microcontroller AT89C51, a LCD and few other electronics components like resistors, capacitors, transistor etc. A LCD is connected to microcontroller through Data pin D0 to D7 as shown in figure. Where a variable resistor VR1 is used to controller the level of contrast. A crystal oscillator is connected to XTAL pin (pin 18 and 19) in order to generate clock frequency. A switch is connected to reset pin of IC1 (pin 9) in order to reset the process. A resistor R5 is used as pull-up resistor in order to control the switch bounce.
Programmable pin P3.7 (17) is connected to base of transistor T2 through resistor R2 in order to switch on the relay RL1. Relay RL1 is used to switch on or off the appliance.
Power supply: The circuit diagram of power supply is shown in figure 4. The input 230V, 50Hz ac input voltage is stepped down to 12V, 50Hz using transformer X1. These 12V output is changed to 12V DC using a bridge rectifier (made from 4 general purpose rectifier diode D1 to D4) and a filter capacitor C4. The filtered 12V DC output is changed to +5V regulated power supply using a series voltage regulator IC (IC4). The power supply circuit shown here can provides two different power supplies (+12V and +5V) as shown in circuit diagram.
Operation: Here we have described how the system operates. The properties and working of switches are listed below in table 1. Switch SW7 is used to select the mode of operation i.e. Single mode or repeat mode. In single mode, the sequence of on and off time will run once but in repeat mode the sequence repeats. When an interruption is occurred during the operation, say when a switch is SW7 is changed to single mode from repeat mode, the time stops only after cycle completes.
In time of emergency, switch SW5 is pressed in order to stop the timer operation.
Function of Switches
|SW1||Start||Start timer operation|
|SW2||Inc. Time||Increment time set by 1 sec. max limit is 60|
|SW3||Dec. Time||Decrement time set by 1 sec. min limit is 1|
|SW4||Enter||Used to enter time set value|
|SW5||ES (RST)||Emergency stop or system reset.|
|SW6||Control Selection||Selection of either remote or keypad control.|
|SW7||Mode Selection||Selection of either repeat or single control.|
Status of Data Input Pins and the Codes Transmitted
Procedure for step by step configuration
- Switch on the device
- A message ‘Enter on time’ will appeared in LCD.
- One can select the desire time by pressing switch SW2 (for decreasing) and SW3 (for increasing).
- Enter switch (SW4) is used to set the time and further ask to enter ‘off’ time same as in setting desire time using switches SW2 and SW3.
- A message ‘Press start’ on display is appeared and operation will start after pressing switch SW1.
- Till on time the relay RL1 energized as a result the device is switch on, when time countdown to zero the relay is de-energized and device will turn off.
Software: Click here to Download Software Code
PARTS LIST OF INDUSTRIAL TIMER CIRCUIT
|Resistors (all ¼-watt, ± 5% Carbon)|
|R1 = 10 KΩ
R2, R3, R7 = 1 KΩ
R4 = 3.9 KΩ
R5 = 47 KΩ
R6, R8 = 330 Ω
VR1 = 10 KΩ Preset
|C1, C2 = 33 pF (Ceramic Disk)
C3 = 1 µF, 16V (Electrolytic Capacitor)
C4 = 1000 µF, 25V (Electrolytic Capacitor)
C5 = 0.1 µF (Ceramic Disk)
|IC1 = AT89C51 Microcontroller
IC2 = HT12D decoder
IC3 = 74LS21 four input AND gate
IC4 = 7805, 5V regulator
IC5 = DT12E encoder
T1 = BC 337 NPN transistor
T2 = BC547 NPN transistor
D1 – D5 = 1N4007 Rectifier Diode
D6 – D13 = 1N4148 Switching Diode
LED1 – LED3 = 5mm LED
LCD = 2-line and 16-character LCD
TX1 = 433MHz ASK Transmitter Module
TX2 = 433MHz ASK Receiver module
|X1 = 230V AC Primary to 12V, 500mA Secondary Transformer
XTAL = 12MHz Crystal
SW1 – SW5, SW10 – S14 = Push-to-on tactile switch
SW8 = 4PDT Toggle Switch
SW9 = SPST Toggle Switch
RL1 = 12V, 1C/O relay