TSOP21..MQ1

Document Number 82249

Rev. 1.1, 31-Jan-05

Vishay Semiconductors

www.vishay.com

5

Suitable Data Format

The circuit of the TSOP21..MQ1 is designed in that

way that unexpected output pulses due to noise or

disturbance signals are avoided. A bandpass filter, an

integrator stage and an automatic gain control are

used to suppress such disturbances.

The distinguishing mark between data signal and dis-

turbance signal are carrier frequency, burst length

and duty cycle.

The data signal should fulfill the following conditions:

• Carrier frequency should be close to center fre-

quency of the bandpass (e.g. 38 kHz).

• Burst length should be 6 cycles/burst or longer.

• After each burst which is between 6 cycles and 70

cycles a gap time of at least 10 cycles is necessary.

• For each burst which is longer than 1.8 ms a corre-

sponding gap time is necessary at some time in the

data stream. This gap time should have at least same

length as the burst.

• Up to 2200 short bursts per second can be received

continuously.

Some examples for suitable data format are: NEC

Code, Toshiba Micom Format, Sharp Code, RC5

Code, RC6 Code, RCMM Code, R-2000 Code,

RECS-80 Code.

When a disturbance signal is applied to the

TSOP21..MQ1 it can still receive the data signal.

However the sensitivity is reduced to that level that no

unexpected pulses will occur.

Some examples for such disturbance signals which

are suppressed by the TSOP21..MQ1 are:

• DC light (e.g. from tungsten bulb or sunlight)

• Continuous signal at 38 kHz or at any other fre-

quency

• Signals from fluorescent lamps with electronic bal-

last (an example of the signal modulation is in the fig-

ure below).

Figure 13. IR Signal from Fluorescent Lamp with low Modulation

0

5

10

15

20

Time ( ms )

16920

IR Signal from fluorescent

lamp with low modulation