pnp sensor on raspberry

Question

how do I hook a PNP sensor to a raspberry pi 3? I know I need an A/D converter, and I've already got a MCP3008. But apart from that, what else do I need? The sensor output switches 24v or 0v, I also know I have to bring it down to 3,3V. Thanks a lot guys!

that assumes it is an analogue sensor. You haven't specified what sensor it is, so how do we know. — Tom Carpenter, May 09 '16 at 11:34

score 2 · Answer 1 · answered May 07 '16 at 16:23

2

The sensor output switches 24 V or 0 V.

That means it's a digital sensor and should be connected to a digital input. You use analog inputs for varying signals which are "analogous" to the physical property you are measuring - e.g., temperature, pressure, etc.

schematic

^{simulate this circuit – Schematic created using CircuitLab}

I also know I have to bring it down to 3,3V.

So we need to divide the voltage by 3.3 / 24 = 7.3. 68k and 10k as shown in Figure 1 should do the job.

The resistor values are high to keep currents low. If you have a two-wire sensor it may need a certain current in the 'off' condition to power the electronics. In that case we may need to scale the resistors down by a factor of 10 or so. Let us know and post a link to the sensor datasheet.

answered May 07 '16 at 16:23

Transistor

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http://www.leuze.com/en/deutschland/produkte/schaltende_sensoren/optische_sensoren/lichtschranken_lichttaster_zylindrisch/baureihe_318_kunststoff/lichttaster/rt_hrt_3/selector.php?supplier_aid=50122564&grp_id=1332237561758&lang=eng#{"tab":"2"} – Roberto Mack May 09 '16 at 02:50
just click on downloads and find the datasheet in your preferred language...
thanks a lot dude! btw I'll still need the a/d for the analog sensors
– Roberto Mack May 09 '16 at 02:51
OK. There's no mention of analog in your question. Industrial analog sensors will be 0 - 10 V or 4 - 20 mA. – Transistor May 09 '16 at 07:27

Spehro Pefhany · Answer 2 · 2016-05-09T04:54:51.333

0

You can use a voltage divider as so:

schematic

^{simulate this circuit – Schematic created using CircuitLab}

It will work with R1 and R4 as a single 30K resistor, with C1 missing, and with R3 shorted, D1, D2 missing, but the suggested parts add more immunity to

edited May 09 '16 at 04:54

answered May 07 '16 at 16:24

Spehro Pefhany

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Invert the diodes before you power on! ;^) – Transistor May 07 '16 at 16:29
D1 is mandatory, right? – Roberto Mack May 09 '16 at 02:53
"Invert the diodes" fixed- thanks ugh. silly mistake – Spehro Pefhany May 09 '16 at 04:55
D1 is not necessarily mandatory if the 24V is regulated and the wires reasonable length, but it's not a bad idea. – Spehro Pefhany May 09 '16 at 04:56

pnp sensor on raspberry

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