DS2438 and HIH4030

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DS2438 and HIH4030

Recently I received the main parts for my one wire, temperature / humidity sensor.

One of maxims DS2438 and Honeywells HIH4030

I'm basing myself on this document:

Once I get the parts to set the smd component on a breadboard I can start testing.

Maybe someone has tested this before? or has input?

Paul's picture
More 1-Wire info

I indeed remember those links from the past. The humidity sensor there was not dallas 1 wire compatible. That's the reason I searched further.

The wiring is attached.
red = +5V
black = GND
Yellow =Data
Please note that you need a 4.7kOhm resistor between the +5V and the data line as with the ds18b20 sensors.

I expected a lot of trouble to get is working but today I bumped into this site:

And my sample script shows (attached):
pi@steven:~$ sudo ./test.pl
$VAR1 = {
'time' => 26,
'humid' => '40.384084135515',
'temp' => '24.375'

I had to change a few values based on my datasheet because he used a 5030

Further investigation needed to get in into the 1 wire driver so it's easily accessible as with the ds18b20 temperature sensors

It seems a good idea to add the extra components to get more stable reads and add shotkeys on the raspberry pi side to safeguard it from spikes.

The costs until now:
- maxim ds2438Z: 7.95 euro
- hih4030 from sparkfun (at a local store) 16.95 euro
- SOIC8 tot dip ( to be able to test on the breadboard) 2.9 euro

I expect that you will be able to find them cheaper.

to be continued ...

Another 1 wire source

Hi, while investigating the best 1 wire solution I bumped into this. Some kind of virtual filesystem to read out Dallas 1 wire chips.

Just for reference:

And an installation guide for the pi:

Paul's picture
need 5 volts/GPIO 7

These sensors appear to use 5 volts. I wonder if they will operate with 3.3 or if newer models will. We have 5 volts on the interface board, but I was hoping to just use 3.3 on the RJ connectors.

DUMB QUESTION: If these are 5 volts devices, with 5 volt data, won't they blow the Pi's 3.3 volt GPIO lines?

Or are you using a USB to 1-Wire convertor?

If connecting directly to to Pi GPIO pins you should probably use RPi GPIO7. There is supposed to be a kernel 1-Wire driver that uses that GPIO. On the version 2 hive interface boards, GPIO 7 was used to control the LED. On the version 3 boards, GPIO7 is brought out to the RJ connectors that the DHT22s plug into, but I didn't put pullups on the line.

variable input voltage

The 1wire ds2438 chip operates from 2.4 to 5 volts.

for the humidity I should switch to the 50xx series. As you can see in these data sheets the minimum voltage for the 40xx series is 4 volts. For the 50xx series it's 2.7. The max voltages are 5.8 and 5.5 so fine in both cases.

I do need to check the accuracy at lower voltages.

Won't we blow the GPIO. Well I guess not, since it's still working now. But I didn't think about that, just because I was doing the same thing as with the ds18b20 sensors. To be double checked!

Indeed GPIO7 is the one I use, no usb converter. They will only drain power :)

It even seems that somewhere in the past someone wrote a driver for the 2.6 kernel:
But it didn't get into the mainstream kernel it seems.

Answer to the question

DUMB QUESTION: If these are 5 volts devices, with 5 volt data, won't they blow the Pi's 3.3 volt GPIO lines?
=> it indeed seems you need to power the 1 wire things with the 3.3 volt line.

I guess i'm lucky I didn't blow my gpio

Thanx for making me aware for this.

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