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Friday, 18 July 2014

Standard Resistor & Capacitor values - Table

By Unknown at Friday, July 18, 2014 circuit ideas, circuit lab, materials, Standard Resistor & Capacitor values - Table 29 comments

The following are the Standard Resistor & Capacitor values.

NOTE: Use this as references for design calculations. Real time application may have differences. These values are std fixed. But actual values may vary depending on the manufacturer's tolerance.

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12V BATTERY HEALTH INDICATOR

By Unknown at Friday, April 11, 2014 12V BATTERY HEALTH INDICATOR, circuit ideas, circuit lab No comments

This circuit is simple and easy to build & has only a few discrete components.
This indicates the 12V battery safe operating voltage.

Diode D1 protects the circuit when the battery polarity is reversed.
The LED glows with full brightness when the battery voltage is above the set threshold.

The threshold is set with the zener diode D2. for this circuit the threshold will
Vds+VBEq1 ~= 11.5V

When the Battery voltage is above 10.8V the LED glows with very little brightness & increases with increase in battery voltage.
When it is above 11.5V the LED glows with full brightness.

The resistance R1 limts the current flow through the LED, R2 limits base current.
The current consumption is very less. Approx 10mA for battery voltage above 13V & very lesser current consumption (in few uA) when battery voltage drops below 10.5V.

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Rectangular Wave - PWM Waveform - Generation using 555

By Unknown at Wednesday, April 09, 2014 circuit ideas, circuit lab 4 comments

This simple circuit that produces a rectangular waveform using the most commonly available analog timer IC 555.

The on time and off time are controlled by the resistances Ra & Rb, which are variable to get the required value.

The formula for the time calculations are

The Circuit diagram is

The rectangular/pwm output is at pin 3 of the IC.
Resistance R1,R2 protects the device from shorting the terminals to VCC and ensure a minimum resistance available between the terminals.

The time delay depends on C2, RV1 & RV2. Change the values for desired output.

To get a square wave output, the condition is Ra=Rb. To get this, set the both pots to extreme left of right.

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About MAX7219 LED Display Dot-matrix Display Driver - Data Format - Register Map - Programming

By Unknown at Saturday, October 26, 2013 About MAX7219 display driver, circuit lab, embedded 2 comments

The Maxim MAX7219

The MAX7219 chip from maxim is a powerful serial input/output common-cathode display driver that interfaces microcontroller to 7-segment numeric LED displays of up to 8 digits and a 8x8 dot-matrix displays. The pindiagram of MAX7219 is (for MAX7221, pin 12 is CS_bar)

Typical application circuit is

Many MAX7219 can be cascaded serially through DOUT pin of one IC to DIN of the another, but with common clock and load connections.

It needs only 3 wires to interface with the microcontroller or microprocessor namely, CLK, LOAD and DIN. It has a build-in BCD (binary code decimal) decoder and a brightness control. It is easy to enable or disable the BCD decoder through the registers. Although the main function is to drive the 8-Digits seven segment LED display but because it also capable to drive an individual LED segment i.e. segment A to segment G and DP (decimal point), by disabling the decoder.

The MAX7219 chip has 16-bit registers divided into two ADDRESS and DATA each of 8 bit size. The data format for programming is

at the negative edge of CLK, the DIN appears at DOUT for cascading

In order to send a command to the MAX7219 chip, first we need send the 8-bits address and next we send the 8-bits data. It uses D8-D11 as address to map 14 registers. The register map is //

//Max7219 Command registers Address
DECODE 0x09 // Decode mode register Address
INTENSITY 0x0A // Intensity register Address
SCAN_LIMIT 0x0B // Scan limit register Address
SHUTDOWN 0x0C // Shutdown register Address
DISPLAY_TEST 0x0F // Display test" register Address
NOP 0x00
D0 0x01
D1 0x02
D2 0x03
D3 0x04
D4 0x05
D5 0x06
D6 0 x07
D7 0x08

The data byte should be proceeded by the address byte.

The segment current is set by an external resistor (Rset) connected to pin 18 and VCC. The intensity can be controlled by software using Intensity register, setting values 1 (min) to 15 (max).

The Shutdown mode turns off all segment drives if its data is 0x00 and normal op if 0x01.

The Display test mode turns on all segment drives if its data is 0x01 and normal op if 0x00.

The Decode register is used to enable BCD decoder for the digits. the values are NONE=0x00, D0=0x01, D0-D3=0x0F, D0-D7=0xFF

The Scan limit register is used to set the number of used digits.

The same principle is also apply to other important MAX7219 chip commands such as activate from the shutdown mode (normal operation), use BCD decode (code B) mode, scanning limit (scanning digit 0 to 7), and adjusting the seven segment LED digit intensity please refer to the Maxim MAX7219 datasheet for the complete explanation.

Click here to download the MAX7219 Datasheet

Comming soon: Interfacing MAX7219 with AVR for 7seg LEDs & later 8x8 dot matrix displays... Stay Tuned. Dont miss it.

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