Electronics lab downloads schematic 013

One of this connector is used for electrical connections, while the other one is used only as mechanical connecting element. The microcontroller controls all functions of device, generates the whole algorithm to control the LED matrix. The LEDs are dynamically controlled row by row. Each one of these IC contain bit serial-in, parallel-out shift register, latch register and 16 constant current output channels.

Outputs are open drain type, allowing connection of a load supplied with up to 20V supply voltage. The constant current for all outputs is set from an external resistor RR connected to pin In this application, the three LED drivers are connected in cascade and controlled from the microcontroller over SPI protocol. The microcontroller sends a bit word, controlling one row at the time.

The 40th bit remains unused. The microcontroller sends this bit word each 1ms. There is 7 row cycles for displaying each row plus one blank cycle, used for process the temperature measurements. Therefore, the refresh rate of display is Hz. Each row cycle begin with logical 0 on OE pin outputs are enabled. Note, that the numbers of columns and rows are not connected in sequential order to the corresponded pins of ICs UU This is done due to simplify the design of PCB.

The real time clock is implemented with U10 — PCF The PCF contains all necessary counter registers to provide real time clock and date information. These features give a possibility to supply the real-time clock for a long time using a small lithium battery or even with a back-up capacitor.

Both options are available in the designed PCB. The footprint for lithium battery is suited for type socket. The experiments using 1F back-up capacitor shows that the clock remain active more than a week after turning-off the power supply.

Trimmer-capacitor C21 is used to adjust the oscillator frequency at Hz. This module is set in I2C master mode. In this case the display will show only built-in messages. For ambient temperature measurement are used LM35 sensors U5, U6. The supply voltage should be between 4 and 30 Volts. To make a full-range temperature measurement, a negative voltage must be applied to the output through a resistor R4 and R5.

To ensure this requirement, the ground pins of the sensors is connected to the analog ground through two diodes VD4,VD5 and VD6,VD7 , which pick them up with approximately 1,4V.

The signal from sensor is taken between the output and negative pins of LM The voltage between these two pins is bipolar with polarity dependant on the measured temperature sign. The sensors could be connected with external three-wire cables. Software is designed to show inside temperature from U6 and outside temperature from U5.

It provides 13 bits resolution 12 bits plus one sign bit. The MCP has 4 analog inputs, which can be configured either as 4 single ended or as 2 differential inputs.

The application requires 2 differential inputs to convert both bipolar voltages from the LM35 temperature sensors. VD8 and VD9 are used for temperature compensation. These lines are under software control from the microcontroller U9. To ensure accuracy analog ground is separated from the digital using small ferrite beam L6. This is an SMD type Z ferrite beam in package.

To increase the accuracy and stability of the indication, a modified average filter is applied. The microcontroller get samples from temperature measurements on each second and the values are stored in a buffer. When 10 measurements are stored, microcontroller subtracts the highest two and the lowest two values.

From remain six values is calculated an average sum. Then to stabilize the display reading, a slight deadband is applied to the average sum. Its output voltage is directly proportional to light intensity on the built in photodiode. To avoid unwanted blinks of display, a slight software delay of PWM control is applied. An additional feature of device is the possibility to be controlled using an Infrared remote control.

It allows device to be installed on a place with difficult access. This protocol is supported from TV Philips. The software decodes the received command and transmits it to the main microcontroller U9 over an asynchronous serial connection.

Vth1, VD14 and R18 realized overvoltage protection. If the voltage of Vcc exceed the zener diode voltage plus thyristor gate voltage the thyristor starts to open and gives short circuit Vcc to ground.

This protects all of integrated circuits from accidentally raising the supply voltage. Note, that the external power supply must have a fuse or current limiter. Of course, this protection circuit is not necessary, but strongly recommended, especially in the stage of testing. Other two power supplies are not so critical if the voltage is increased. It is necessary to pay attention to the Vled voltage.

Its value is very important due to the power dissipation from the LED drivers. For reliable work the Vled should be 0,,7 higher than the Vf. But not to be much more higher, because the power dissipation from the drivers will increase and a thermal shut-down protection will be activated. To calculate the Vled use the next formula:. It is also need to choose a proper value for LEDs current.

The showed value set the current at approximately 80mA per output. The available buttons from IR remote control are as follows:. After Power on the display enters in normal mode of operation, showing continuously the last selected message. The values for temperatures are unavailable for the first 10 seconds. If this message is shown after this period, it is an indication for a fault temperature sensor.

If an external EEPROM not installed or the selected number is empty or deleted the display will load a message from built-in memory.

At first time the display will show Maximum or Minimum reached Outside temperature. In five seconds the display will return in normal mode of operation. In normal mode of operation press two times SET button. With a new version re-written from scratch being released by the end of , we are revisiting it now.

Although at first sight, we can spot quite a few similarities in regards to the UI, there is now more features and very useful ones , better user The Upverter tool Skip to content Home Software. Continue Reading 13 January, 1. Continue Reading 8 December, 1. Continue Reading 16 November, 1. Continue Reading 21 October, 1. Continue Reading 23 September, 2. Continue Reading 4 May, 2. Continue Reading 31 March, 1.