TSL1401 how to connect sensor

analogbody

I am beginner. I have no idea how to connect some of the pins and I think there is no answer in any datasheet.
Precisely I want to know what to do with:
VDD
TR
SD
ST
SI
GND
SO
SC
CK
AO
+5

Of course I know that i have to connect three signals
SI, AO, CLK
of course GND -0 and +5
and probably VDD to +5

but rest??

could you describe everything very precisely?
Piter

Phil Pilgrim (PhiPi)

You don't need to connect anything but Vdd, Gnd, SI, CK, and AO. The other signals pertain mostly to the mezzanine connector, which can be used for strobes or syncing to external illumination sources.

-Phil

Martin_H

Phil, I looked at the product sheet and it looks like the TSL1401 can work with either 3.3 or 5 volts. When operating at 3.3 volts do you need to change exposure times, or does it figure all that out? I assume the analog output goes from 0 to 3.3 volts so I can send it to a Propeller chip at that point.

Phil Pilgrim (PhiPi)

Martin,

Supply voltage and exposure time are independent. Regardless of the supply voltage, the same amount of light exposure will produce the same output voltage. The only difference is that, with a 3.3V supply, the output will saturate sooner than with a 5V supply. Because of that, if you're using an ADC whose reference voltage is Vdd, the TSL1401 will appear to be more sensitive by about 50% at Vdd = 3.3V than at 5V. But that's a function of the ADC, not the sensor.

-Phil

Martin_H

Thanks Phil. I definitely planned to use the PropBOE's built in ADC, so good to know about the faster saturation. I'll just reduce exposure times.

Martin_H

Quick sanity check please.

With the stamp both Vdd and the 5 volts pins of the DB expander are connected to 5 volts. But with the Propeller I connected Vdd to 3.3 volts and 5 volts to 5 volts. This runs the camera off 3.3 volts and A0 can connect to the ADC on the Prop Boe, but 5 volts is available in the mezzanine connector for my transistor controlled super bright LED. The transistor will be switched on by a Propeller pin, but the LED gets its power from 5 volts through a resistor.

Basically I don't want to let any magic smoke out of the Prop BOE since I am mixing 5 volts and 3.3 volts in this manner.

Phil Pilgrim (PhiPi)

As long as you're switching the LED with a transistor (NPN or nMOSFET), you should be okay. Also, you can connect the TSL1401-DB's Vdd pin to +5V without a problem. Its inputs have TTL characteristics, and the PropBOE's ADC is referenced to +5V. So you will get a better full ADC range from AO if you do it that way. I'm working on a proto PropBOE add-on board that uses the TSL1401 and am powering it from +5V for that reason.

-Phil

Martin_H

Thanks Phil that's even simpler.

Martin_H

Rather than use the ADC, I want to use pin 0 and threshold the pixels on the Propeller like I do with the BS2. Should I run the TSL1401 off 3.3 volts, 5 volts with a current limit resistor, or is the analog output low current?

Phil Pilgrim (PhiPi)

Run it from 3.3V There's no advantage in going to 5V.

-Phil

Martin_H

Phil Pilgrim (PhiPi) wrote: »

Run it from 3.3V There's no advantage in going to 5V.

Thanks Phil. I shall try this tonight.