Strange measurment of Pololu Carrier with Sharp GP2Y0A60SZLF


I’use about 20pcs of Pololu Carrier with Sharp GP2Y0A60SZLF Analog Distance Sensor 10-150cm, 3V
2 pcs by PCB, battery powered by LS33600 (Saft), max pulse 250mA, the 2 pololu are directly connected to battery, without resitor, capacity.
Only one GP2Y0A60SZLF is wake at the same time:

[code] wake_IR(IR1_pin_sleep); sleep_IR(IR2_pin_sleep); delay(10);
sensorValue = analogRead(IR1_pin_data);

wake_IR(IR2_pin_sleep); delay(10);
sensorValue2 = analogRead(IR2_pin_data);

The result is very strange for some pcb, sensorValue are very chaotic.
[ul]For example average, oriented to infinite, “normaly” sensorValue between 0 and 180; when you cut the signal by pasing near 30cm, sensorValue between average 6 cycles give between 250 to 600.
My problem : for some PCB, oriented to infinite, it’s very chaotic, 0, 300, 90, 270, 100, 350, etc…[/ul]
I don’t know why ???
Somone could help me ?
Best regards


I did a quick search for that battery and the one I found (a Saft LS33600 Lithium-Thionyl chloride, Li-SOCl2, chemistry cell) was designed to be used with loads of a few microamps over long-term time periods (3 to 15 years). A battery like that might have trouble keeping a stable supply voltage with the high periodic load of the emitter on the sensor being drawn from it.

Although the peak current draw of the sensor is not listed in its datasheet, it will be several times higher than the listed Average supply current (33 to 50 mA) and it is possible that is very close to or exceeds the 250mA maximum rating for your battery. You might try testing with a different power supply like a benchtop supply to see if you get better behavior. Placing a large electrolytic capacitor near the sensor board between VCC and GND could help stabilize your readings, though this will depend on the characteristics of your power supply. You should also keep in mind that the voltage measurements on the analog pins of the Pro Mini will also be related to the input voltage there, so adding an electrolytic capacitor near to your board might also help stabilize your measurements as well.

Finally, you might try increasing the delay between waking and reading the sensor to something like 100ms. The timing chart on page 5 of the datasheet, seems to indicate that the output will be unstable when the sensor first wakes up.