CNY70 from 5V to 3.3V

Question

I have CNY70 connected this way:

And I need to determine the value of R2 for OUT to be from 0V to 3.3V. I don't know how to calculate it, please help.

EDIT: Input is the 5V and output goes to microcontroller similar to Arduino, but its inputs can't take Voltage higher than 3.3V. So I need to get the output to 0V - 3.3V. I am sorry for being misleading.

EDIT 2: It goes into one of the microcontroller's analog inputs. Not the power supply.

Thank You!

What are you trying to do? That doesn't look like a reliable way to get 3.3V as an output. — JRE, Aug 04 '20 at 15:12
short pins 3 and 4 ... why do you believe that any resistor would cause the output to be 3.3 V? — jsotola, Aug 04 '20 at 15:18
Again, what are you trying to do? Do you need 3.3V to power some other device? Do you need a 3.3V digital signal from a 5V digital signal? Do you need to convert an analog signal that varies between 0 and 5V to an analog signal that varies between 0 and 3.3V? What is your input, and where does the output go? — JRE, Aug 04 '20 at 15:27
@JRE Input is the 5V and output goes to microcontroller similar to Arduino, but its inputs can't take Voltage higher than 3.3V. — Wojtic, Aug 04 '20 at 15:32
Then this is a whole lot easier, and it doesn't take an optoisolator to do it. Add those details to your question. — JRE, Aug 04 '20 at 15:44
@Andyaka What are better ways to detect black and white on some board? — Wojtic, Aug 04 '20 at 16:16
Why do you believe you need to use an opto-isolator? I can play this game all day. — Andy aka, Aug 04 '20 at 16:18
Connect the opto collector to the MCU +3.3 volts rather than to +5V. — Peter Bennett, Aug 04 '20 at 16:19
What you found as a solution to one problem has become the source of another problem. — Andy aka, Aug 04 '20 at 16:21
@PeterBennett I am supplying it all with 5V. I can't do that. — Wojtic, Aug 04 '20 at 16:22
@Wojtic: Your 3.3V microprocessor has a 3.3V power supply **somewhere.** Use it with the phototransistor from the CNY70. — JRE, Aug 04 '20 at 16:25
@JRE Then I wouldn't need to use R2 at all? I will probably do it this way. I was just wondering if there wasn't an easier way to do it with 5V. — Wojtic, Aug 04 '20 at 16:27
Comments are not for extended discussion; this conversation has been [moved to chat](https://chat.stackexchange.com/rooms/111415/discussion-on-question-by-wojtic-cny70-from-5v-to-3-3v). — Voltage Spike, Aug 04 '20 at 17:06

Spehro Pefhany · Accepted Answer · 2020-08-04T16:38:39.960

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You cannot do it by modifying the value of R2.

You can add a series 510\$\Omega\$ resistor between the +5 and the reflective sensor collector.

edited Aug 04 '20 at 16:38

answered Aug 04 '20 at 16:37

Spehro Pefhany

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So the value of R2 will stay 1k? – Wojtic Aug 04 '20 at 16:38
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Yes, it must stay 1K. If you find the sensor is not sensitive enough, increase both resistors proportionally. Eg. 1.5K and 3K. – Spehro Pefhany Aug 04 '20 at 16:39
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Thank you so much. This should solve my problem. – Wojtic Aug 04 '20 at 16:40
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@Wojtic You are welcome, and welcome to the site. By the way, it's good practice to link the datasheet for your parts such as the [CNY70](https://www.vishay.com/docs/83751/cny70.pdf) which would have made it more clear what you are trying to do. – Spehro Pefhany Aug 04 '20 at 16:51

CNY70 from 5V to 3.3V

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