Replacement for SHT75 temperature sensor - Page 1
Forum section: electronics / repair

author: james_s
author_rank: Super Contributor
timestamp: January 09, 2021, 11:39:07 pm
content: I'm working on a veterinary incubator that has a damaged sensor (bodily fluids and resulting nasty corrosion), it's a Sensirion SHT75 which unfortunately has gone obsolete. Is anyone aware of a compatible replacement? I don't mind adapting the mounting or wiring but I do not have access to the firmware for the controller so I need something that will work with it. There are some Chinese ebay sellers that have some pieces listed but when I've bought obsolete parts from sellers like that in the past I've had a nearly 100% rate of being scammed with fakes.

author: fzabkar
author_rank: Super Contributor
timestamp: January 10, 2021, 12:03:48 am
content: FWIW, SHT15 is the smt version.A Google search suggests that Farnell may have the SHT75 sensor, but the web site is down ATM.If I go here ...https://www.newark.com/sensirion/sht75/humidity-temperature-sensor-sip/dp/18M2988... I am offered an alternative part from Avnet (CC2D25-SIP by Amphenol / Telaire):https://www.newark.com/amphenol-advanced-sensors/cc2d25-sip/humiditytemp-sensor-rohs-compliant/dp/84AC0948Datasheet:http://www.farnell.com/datasheets/1855931.pdfEdit: I just noticed that the MOQ is 100. :-(

author: james_s
author_rank: Super Contributor
timestamp: January 10, 2021, 12:28:51 am
content: That page loads for me but the stock is 0 and it says unavailable. They suggest the SHT85 as a replacement which would be great if I were designing a new product but I need something to work with the existing system. The CC2D25-SIP also looks like it is a suggested replacement for new designs and not directly compatible. This highlights a real problem with the various digital sensors that are so popular now, they get discontinued and companies don't bother to include a compatibility mode in successors. If I needed to replace a 10k NTC in a piece of equipment twice as old as this one I could buy one today for under 50 cents.If anyone happens to have a SHT75 lying around I'd be happy to pay a fair price for it, this is a paid job and I can invoice the client for the part. I don't want to waste a month waiting for a part from China only to discover it's counterfeit junk.

author: testpoint1
author_rank: Frequent Contributor
timestamp: January 11, 2021, 03:41:56 am
content: you can use the SHT71 (+-3.5%) , it is quite cheap:https://www.ebay.com/itm/SHT71-SENSIRION-Humidity-Temperature-Sensor-0-100-RH-Digital-3/174164870573

author: aheid
author_rank: Regular Contributor
timestamp: January 11, 2021, 03:46:19 am
content: Surely it couldn't take that much to support both the old protocol and i2c in the same package. The old protocol specifies pullup on data line only, so should be possible to add a pulldown on clock line to signal old protocol, no?

author: james_s
author_rank: Super Contributor
timestamp: January 11, 2021, 06:38:19 pm
content: Thanks, I'll have to grab the datasheets and see what the difference is between the SHT71 and the SHT75. This is for a medical (veterinary) incubator so I want to make sure it works the same as it did previously. A new unit is around $10k so it's worth repairing this one.

author: james_s
author_rank: Super Contributor
timestamp: January 18, 2021, 08:50:13 am
content: So I picked up one of those SHT71 sensors, and then upon looking more closely at the original I realized that it's also a SHT71 despite the reference designation on the PCB saying SHT75. The replacement sensor works perfectly and it's not reading the correct temperature instead of 999F. I'm tempted to try to shield the sensor to prevent future failure since these won't be available forever. Usually animals are in dire shape by the time they need go into this thing so errant fluids are not uncommon.