Creating Pixel LED Using TM1812

TM1812 is a 12 output RGB LED drive IC , which means single TM1812 IC can drive 4 RGB LEDs.This IC consists of data latch , signal reshape and high voltage regulator circuits. It can be used for outdoor large-screen and color dot-matrix control applications.Since it can control 4 RGB LEDs  ,this IC is most suitable for designing pixel LED strips .

 

 

How TM1812 Chip Works 

TM1812 Internal Block Diagram

The chip uses a single-wire communication method called non-return-to-zero (NRZ) for communication. After the chip is powered on and reset, it receives data through DIN pin from the pixel LED controller .

After receiving 4 sets of 24 bits of data (total of 96 bits), the DOUT port will forward data next data to the next chip to provide input data for other TM1812 chips. Before forwarding, DOUT  pin kept in pull down state. If the input signal at DIN is the RESET signal,The chip will not receive new data, The chip will set the FET's gate voltages of each output channel according to the received data . Chip will receive new data after the signal ends until the next reset signal .

After receiving the first 4 sets of 24bit data, the chip will communicate Data is forwarded through the DOUT port.The chip adopts automatic shaping and forwarding technology, which can completely avoid signal attenuation and distortion when transmitting more points over long distances, making the number of chips in the network is not limited by signal transmission, but only limited by the speed of the data transmission.

Features of TM1812 Chip

• CMOS Technology .
• Input voltage support up tp 24v (with the help of external resistor)
• Brightness adjustment circuit ( 256 levels of brightness)
• Single-wire communication (NRZ).
• Built-in signal reshape circuit.
• Built-in RC oscillation and clock synchronization circuit.
• Built-in power-on reset circuit
• The PWM control terminal can achieve 256-level adjustment.
• Data transmission speed up to 800Kbps
• Package form: SOP16, DIP16 .

TM1812 Circuit Diagram 

TM1812 Circuit Diagram 5v

TM1812 Circuit Diagram 5v

In this circuit , TM1812 IC  powered by a 5v supply.Three common anode RGB LEDs being connected to the output pins of the TM1812 IC you can also use RGB LEDs without common pins. The 104 (0.1uf) non-polarize capacitor work as a bypass capacitor to ground any AC components in the power rail , Two resistors (R2,R3) are connected at the data input and output pins to match the impedance (Optional)  ,You can use a resistor between 100Ohm - 200Ohm.

TM1803 Circuit Diagram High voltage

TM1803 pixel LED Diagram HV

In this circuit diagram the supply voltage is grater than 5v (6v-24v). Since the three RGB LEDs are connected to voltage over 5v ,current limitting resistors (R1,R4,R5,R6,R7,R8,R9,R10,R11,R12,R13,R14) in series with the RGB LED pins being used.The value of these resistors can be calculated using the equation.

Rled = VRled / Iled

Rled  in this case  the resistor value .Iled is the current flow through the LED. VRled In this case Voltage drop between resistor pins which is [ Vs - Vled ] (Vled means the voltage drop between LED's anode and cathode). These values can be measured using a multi-meter or referring the datasheets of the RGB LED.As you can see in the diagram , you can use multiple LEDs in series with TM1812 pixel LED IC.

In order to protect the IC from higher supply voltages a resistor (R2) in series with the (VDD) pin is being used .The value of that resistor can be calculated using the below equation .

 R1 = VR1 / I 

Where "VR1" is [ Vs (supply voltage) - 5v ]  and "I" equals 1mA . eg - If the supply voltage is 6v the R2 value should be 1Kohm ,  if the supply voltage is 9v the R2 value should be 4Kohm .Here is a list of resistor values for different supply voltage levels.

TM1812 pixel led resistor values

The 104 (0.1uf) non-polarize capacitor.It work as a bypass capacitor to ground any AC components in the power rail , Two resistors (R2,R3) are connected at the data input and output pins to match the impedance (Optional)  You can use a resistor between 100Ohm - 200Ohm.

TM1812 Pixel LED PCB

 

TM1812 Pixel LED PCB

• Q1 - TM1809 IC (SOP16)

• R2 ,R3  - 0.1 W (8050)

• C1 - 0.1uf (Ceramic Non-polarized Capacitor 1206 ) 

This is a 21mm x 16mm (WxH) PCB designed only using SMD components. IC package is SOP16 .The resisters (R2,R3) are 0.1 watt 8050 package. SMD pads are being used for the input , output and RGB LED connections."COM" pads are where the common pin of the RGB LED should be soldered .Use the Gerber files if you wants the PCB to be manufactured by a PCB manufacturer like JLPCB. 

[ Download the Proteus Project and Gerber Files ]

5050 RGB LED with TM1812 IC

TM1812 5050 RGB LED PCB

This PCB is design to use as Pixel LED strip by soldering one unit to the other in series.D1 ,D2 ,D3 ,D4 are RGB 5050 package LED's.The resisters (R2,R3) are 0.1 watt 8050 package . C1 is a 0.1uf Ceramic Non-polarized Capacitor 1206 package.

5050 RGB LED PCB layout

 

The above image shows the PCB layout of the 5050 RGB chip used in this pixel LED PCB . When you are purchasing a RGB LED for this PCB , Please ask for the datasheet of the RGB LED from the vendor and refer it's PCB layout . No need to match  the order of three color LEDs , Because you can always change the order of the RGB channel signals from the software .Eg - In LEDEdit software you can change the color channel sequence in the new project window. If the polarity of the 5050 LED you purchased is opposite from this one , Turn the LED 180 degrees and solder it.

 

How to use TM1812 PCB

TM1812 5V Wiring Diagram

As you can see in the diagram each TM1812 pixel led unit soldered with three RGB LED's .The pixel LED controller connects to the first pixel LED unit , Data terminal of the controller connects to the Data IN of the first pixel led unit.The 5v and ground of the controller connects to the +5v and GND of the first pixel LED unit respectively.

DOUT of the first pixel LED unit connects to the DIN of the next pixel LED unit.The 5v and GND of the first pixel LED unit connects to the +5v and GND of the next pixel LED unit respectively.Like wise each pixel LED unit connects in series .The number of the units only limited by the pixel LED controller capabilities.

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