Replacing Photodiodes/ LED on Smart Sleeve

Hardware Smart Sleeve
1

Goal

In this tutorial, we are teach how to replace photodiodes and LEDs when the optical density traces don’t look ideal.

Why?

So why would the parts be variable? Well mainly because we are using inexpensive parts for eVOLVER Smart Sleeves, which ends up being great due to the affordability and accessibility to tinker with/ redesign. The disadvantage comes with the potential for variable behavior of some parts. Sometimes, after calibration, we will notice that parts installed aren’t optimal and we need to replace them.

For example, the following OD trace is non-ideal: How do we fix it?

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Parts Needed

Tutorial

1) Locating LED/ Photodiodes

Typically, there is one IR LED and two IR photodiode in each setup. The two photodiodes collect light at different angles, resulting in much better dynamic range. When the calibration curve looks noisy (like shown above) the most likely fix is to switch out the photodiode. Sometimes, but more rarely, the LED is the culprit.

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2) Switching out screw terminal parts (IR LED, 90 Degree Photodiode)

To switch out any parts that are mounted via screw terminal, it is very simple and straight forward. You can simply unscrew the part with the small screw driver and replace the part. Make sure that the LONG END goes to PWR (+).

IR LED

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IR Photodiode

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3) Switching out soldered parts (135 Degree Photodiode)

Dealing with soldered parts are more work but still fairly easy. If you need a quick tutorial on soldering, please refer to this nice guide from Sparkfun.

Generally, I like to use a solder wick. If you heat up the solder next to the wick, the solder will be “soaked up” and wicked away. See pictures below.

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4) Insert photodiodes/LEDs back into the slot

Make sure the diodes are back into the 5 mm holes. Don’t insert the diode too deeply into the 3D printed part. This may obstruct the glass vessel.

That’s it! Plug it back into eVOLVER and recalibrate the sleeve!

4 Likes
2

Hi Brandon,
What is the part number or link for the thermistors?
Thanks.

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954-103JT-025

Good luck!

4

I can’t seem to find the Lite-On photodiodes (LTR-323DB) anywhere right now. Would it be ok to use similar products from other manufacturers? If so are there reliable manufacturers that you recommend?

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I’m also curious about this

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Hi Eric,

I found the LTR-323DB here: LTR-323DB in Bag by LITEON | Photodetectors (Infrared Detectors) | Future Electronics

I think in general you can use any photodiode with a similar wavelength sensitivity profile. This might require tuning of the LED power levels/resistor pack though, so it’s best to continue using the same PD/LED pair if possible as these have been thoroughly tested and characterized by both us and others in the eVOLVER community.

Zack

1 Like
7

Hi All,

Quick question! I have one vial with poor OD readings (chaotic instead of a line), I have replaced the photodiodes, and I am now testing with a water vial.

It seems like if my replacement fixed the issue, the OD readings would be a stable line (but just generally wrong since I have not recalibrated yet). In my case, the OD readings are still very chaotic after the replacement, so I am thinking the problem is still there, and perhaps I will change LED next.

Conversely, does a newly connected sleeve have to be calibrated to get rid of the chaotic OD readings? I think I have observed this before but can’t quite remember, and wanted to ask since it can save a lot of time with troubleshooting.

Thank you!
Katie

8

Generally if you see a noisy RAW value of the sensor, the readings will also be noisy. Calibrating the sleeve will still lead to a noisy result.

You can just run an experiment (with water + stirring, turn off any pump feedback) and look at the raw values that come in and how they compare across good/bad sleeves. If it is super noisy there, then you should probably swap.

I would definitely change out the LED (and even the PD again, if swapping the LED doesn’t fix it). The LED and PD are cheap, and thus might not have super tight tolerances.

Best,
Brandon

1 Like