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Rickard5

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Joined: 31/03/2022
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Posted: 05:58pm 17 Apr 2022

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Hello everybody I'm trying to figure out how to hookup the HC-SR04 o the Picomite and the only info I found was from the manual :

Quote Using a HC-SR04 ultrasonic sensor and the DISTANCE() function you can measure the distance to a target.
Any PicoMite I/O Pin
On the PicoMite you use the DISTANCE function as follows:
d = DISTANCE(trig, echo)
The value returned is the distance in centimetres to the target.
Where trig is the I/O pin connected to the "trig" input of the sensor and echo is the pin connected the "echo" output of the sensor. You can also use 3-pin devices and in that case only one pin number is specified. The maximum voltage on the PicoMite�s I/O pins is 3.3V so a resistor divider will be required to interface the PicoMite to the echo pin of the sensor (which operates on 5V).

my question is, so how do I build this Resistor Divider? and what pins do I use ?

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Tinine
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Joined: 30/03/2016
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Posted: 08:34pm 17 Apr 2022

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This is from my Android app "Electrodoc" (nice).

Play with combinations that suit what you have in stock or whatever power dissipation you want to shoot for.

Craig

Mixtel90

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Joined: 05/10/2019
Location: United Kingdom
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Posted: 09:00pm 17 Apr 2022

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I doubt if the Pico input will load that with 165R!

Try 3.3K on top and 6.8K on the bottom to give 3.366V off-load. The Pico input is pretty high resistance but that is safe and will drop a little further.

Mick

Zilog Inside! nascom.info for Nascom & Gemini
Preliminary MMBasic docs & my PCB designs

Rickard5

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Posted: 09:57pm 17 Apr 2022

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so VCC goes Strait to 5v pin
GND goes strait to GND pin
ECHO goes straight to an input
and Trig goes through visitor ladder ?
Thanks Guys
I feel Dumb but I don't know

I may be Vulgar, but , while I'm poor, I'm Industrious, Honest, and trustworthy! I Know my Place

TassyJim

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Joined: 07/08/2011
Location: Australia
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Posted: 10:20pm 17 Apr 2022

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Rickard5 said so VCC goes Strait to 5v pin
GND goes strait to GND pin
ECHO goes straight to an input
and Trig goes through visitor ladder ?
Thanks Guys
I feel Dumb but I don't know

TRIGGER goes straight to an output
and ECHO goes through resistor ladder to input

VK7JH
MMedit

Rickard5

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Joined: 31/03/2022
Location: United States
Posts: 463

Posted: 11:12pm 17 Apr 2022

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OK Cool Thanks Jim now I just have to go though the unenviable task of sorting though the mega box of Resistors looking for 3.3 K and 6.8k resistors :)2 then I'm off to try it :)

I may be Vulgar, but , while I'm poor, I'm Industrious, Honest, and trustworthy! I Know my Place

phil99

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Joined: 11/02/2018
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Posts: 2640

Posted: 12:12am 18 Apr 2022

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Getting the exact resistors isn't very important. Just make the bottom one twice the value (or a little less to be safe) of the top one.
Other examples:-
5.1k, 10k
12k, 22k
2.7k, 5.1k

The required voltage ratio is

3.3 / 5 = 2/3

So you can use any three of the same value in series to get an exact division of 2/3.

KD5ZXG
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Joined: 21/01/2022
Location: United States
Posts: 53

Posted: 02:37am 18 Apr 2022

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Cut 5V simply in half works fine too.
Anything over 2V is probably logic true.
You can hit anywhere from there to 3.3V.
Edited 2022-04-18 12:39 by KD5ZXG

Mixtel90

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Joined: 05/10/2019
Location: United Kingdom
Posts: 7937

Posted: 06:33am 18 Apr 2022

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Using 50% is borderline and there's no real need to do it. It increases problems due to noise on the signal and supply lines. e.g. you have a Pico input that happens to need 2.1v (within spec). If you use 50% then you have to guarantee an output of 4.2V. If your "5V" rail is at 4.7V then that may not be possible.

Also, don't use too high a value if using a potential divider for level shifting into MOS logic. Inputs have a high impedance and capacitance so high resistor values will slow the logic down. That can lead to all sorts of interesting bugs to find. :) You generally have plenty of current to spare so use it. Why use a 10uA divider when you can use a 1mA one?

Mick

Zilog Inside! nascom.info for Nascom & Gemini
Preliminary MMBasic docs & my PCB designs

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