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. — 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 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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