Friday, 4 December 2020

Inside an AMG8833 thermal imager

Very simple AMG8833 thermal imager

(I took it through it's paces in this video)

For years I had felt he need for a thermal imager or thermal camera to help me find faulty electronic components. But the price tag was prohibitive.

40mA - not very power hungry

I experimented with a single temperature sensor, sweeping a range with model servos. Interesting and entertaining, but not really useful. That was back in 2013. Even later, the cost for the simplest "grid eye" was still a bit on the high side for an experimenter. Until recently.

Bare bones imager

I then found this bare bones / no frills thermal camera here on Banggood. It comes without any matching documentation, let alone a manufacturer name.

PCB Version 5.1.2 from June2020

It has a resolution of 8x8 pixels and sports the "high gain" version of the Grideye. While "high gain" sounds like a good thing, it actually limits the sensor's thermal range to 0-80 degree centigrade.

The AMG8833

The Panasonic GridEye comes in different flavours that is easy to decipher from the part number:

The 88 stands for the 8x8 pixel resolution, the next digit shows the operating voltage 5 for 5volts, 3 for 3.3 volts. And finally a 3 for the "high gain" and a 4 for the "low gain" version, with the low gain version ranging from -20C to 100C. We don't have that in this device so on very cold days, the outside world looks like a blank sheet to the imager.

The next step up is the 32x24 pixels MLX90640 from Melexis, which has a -40 to 300C temperature range. Looking at what 8x8 pixels can do, 32x24 should be awesome. It comes at about twice the cost of the AMG8833 based imager, also from Banggood.

Electronics repair

It all boils down to the question: are 8x8 pixels sufficient to identify hotspots in a faulty device?

44c after just a few seconds
With it's 60degree field of view, working close-up gives enough contrast to identify individual hotspots. One thing to notice is that the colour scheme is autoscaling. So "red" just means warmer than the surrounding area, not necessarity hot. The colors are spread over the range currently detected by the sensor. The good aspect is that it always gives the best contrast possible, the downside is, that it can be very irritating.

The microcontroller

The GD32 ARM Cortex-M3 Microcontroller

Quite a capable little 32-bit RISC microcontroller from GigaDevice's "Value Line". See the data sheet here for details. The GD32F130F4P6 is the simplest of the DG32F130Fx family in the TSSOP20 package, sporting 16kByte of flash memory.
This thing appears to be pretty much a clone of the STM32F103x4 and might well be programmable with a ST-Link programmer. (haven't tested that).
The earlier 1.1 version, for which Banggood has a schematic diagram available, had a STM32F103C8, which essentially has the same performance, but more (64KBytes) of flash memory. So they obviously cut costs here a little on their way to Version 5.1.2

Final words

At a price point around 50 EUR/USD, this is not only a great experimenter's gadget, but very useful to track down thermal problems. Certainly no match for a full blown thermal camera, possibly even with a visual overlay - the cheapest models starting at three times the cost of this device.
The 0-80C temperature range can also be a maior limitation, depending on the intended use.
For me it is way better than sniffing out hotspots on PCBs or burning my fingers on them.

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