Testing the IRPD

Lynxmotion
1

hello
the IRPD sensor i bought , when tested without controller makes the status led on if enable pin is given 5v even in the absence of obstacle. applied electrical tape around the ir led and on three sides of detector as mentioned in the manual still the problem exists.

when tried to observe the output at different point of the circuit. at the 8th pin of ic 74HC00 i.e., nand gate output of the oscillator part is only 18khz and not 38khz.

and as soon as enable pin is applied 5v the detector goes low and hence the status led becomes on.

plz suggest me what i should do to make my sensor work as desired.

2

Completely cover up the detector and then connect power to the enable line. If the status LED lights, your IR sensor output may be grounded. If do the same test with the IR sensor output not connected to anything and then if the status LED lights, the detector may be bad.

3

i covered the detector completely and powered the enable pin even then the status led lits.

4

Is the IR sensor output connected to anything?

5

The IRPD can be fussy to set up and troubleshoot. If it’s just defective we can ship you a replacement when we get back from our break.

6

hi
i got the sensor working perfectly also connected it to the OOPic-R board and tested it.

can you explain me the logic behind nand gate functioning as oscillator.

74HC00 is an quad2 input nand gate ic. 14th pin is given supply of 5v. 7th pin is grounded. 12th and 13th pin are shorted and its output is given to 9th and 10th pins with both shorted and 8th pin output is fed back to 13th pin via capacitor and a resistor…

now if we assume initially 12 and 13 pins are at ‘0’ then its output at 11th pin is high i.e., ‘1’. which is given to pin 10 and 9 and hence its output at pin 8 will be’0’ but if this is the case then this output is fed to pin 2 and 5 of other two nand gates, whatever may be other input to the nand gate its output will be high because one of the input is ‘0’. and the IR LED connected to it should not emit light. this is not the case the IR led emits light when other input is enabled. it means the feedback from 8th pin must be ‘1’ . this is possible if 12 and 13th pin is at ‘1’ and their output is’0’. but we are not connecting the 12 or 13 pin to 5v as observed from circuit diagram.

can u please explain me the logic behind it .

7

The two NAND gates make a 38khz oscillator. The output going to pins 2 and 5 are high for 26uS then low for 26uS. :wink: It’s a free-running oscillator. It’s job is to modulate the infrared LEDs when they are enabled by to another two inputs. It’s not intended to enable or disable the outputs…