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lizby
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Joined: 17/05/2016
Location: United States
Posts: 3478

Posted: 05:53pm 20 Jul 2021

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Riddle me this.

I got one of the neat SR04P Ultrasonic Distance Sensor with 7-Segment displays.

The display shows the distance in centimeters--tracking very nicely as I move my hand back and forth. At 9600 baud, it's supposed to transmit distance in the form of D:nnn from a few to about 400cm.

On my Picomite, I entered

SetPin 21,uart0tx:SetPin 22,uart0rx : Open "com0:9600" As #1
do: if loc(#1)>7 then: a$=input$(7,#1): ?a$;: endif: loop

I get either dashes or garbage: "jR[]" (where [] is a solid block).

I connected it to my laptop with a CH341 serial ttl module. In TeraTerm, it displays the distances. I connected it to an F4, and that displays the distances. I made a 3-way splitter and while connected to the Picomite, also connected to the PC with the CH341, and both Teraterm and the Picomite display the distances.

Do I need a pullup or pulldown on the Picomite? Why?

Note: the website documentation says the module is 5V, but the 7-segment display is fine with the Picomite 3v3, and the serial is fine with 3V3 on both the F4 and the CH341. (Some websites say that the newer version (which I probably have) works fine on 3V3.)

~
Edited 2021-07-21 03:55 by lizby

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phil99

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Joined: 11/02/2018
Location: Australia
Posts: 2831

Posted: 12:55am 21 Jul 2021

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As TTL serial is active low, try a 4k7 to 10k pullup and see what happens. It can't hurt to try.

lizby
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Joined: 17/05/2016
Location: United States
Posts: 3478

Posted: 01:33am 21 Jul 2021

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phil99 said As TTL serial is active low, try a 4k7 to 10k pullup and see what happens. It can't hurt to try.

10K pullup did the trick. Thanks very much.

Now the question is, why, when the CH341 and F4 didn't need it, and an ESP-01 works perfectly on the same picomite serial port.

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matherp
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Joined: 11/12/2012
Location: United Kingdom
Posts: 10610

Posted: 07:57am 21 Jul 2021

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Please try the attached without the pullup resistor

PicoMiteV5.07.00b4.zip

Most versions of MMBasic enable an internal pullup on serial RX. This isn't part of the spec and shouldn't be necessary but I think I've added it to the Picomite although the datasheet is a bit unclear as to whether special functions like serial and pullups are mutually exclusive

lizby
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Joined: 17/05/2016
Location: United States
Posts: 3478

Posted: 11:41am 21 Jul 2021

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matherp said Please try the attached without the pullup resistor

That worked--thank you very much.

This prints the distance whenever it changes:

PicoMite MMBasic Version 5.07.00b4
Copyright 2011-2021 Geoff Graham
Copyright 2016-2021 Peter Mather
SetPin 21,uart0tx:SetPin 22,uart0rx : Open "com0:9600" As #1 ' (ultrasonic module)
do: if loc(#1)>7 then: a$=input$(7,#1): if b$<>a$ then: b$=a$: ?a$;: endif: endif: loop

D:333
D:249
D:025
D:020
D:016
D:015
D:056
D:019
D:036
D:018
D:050
D:011
D:014
D:012
D:010

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