Cam­era Investigation

Some minor updates on the cam­era invest­ig­a­tion front. The Seek Thermal cam­era has arrived and I have had a brief play with it. It is nice, my only cri­ti­cism is that the res­ol­u­tion sits in an uncom­fort­able spot. The res­ol­u­tion is far higher than pre­vi­ous thermal cam­eras with the very big blocks of data, it looks much more like a nor­mal cam­era. Which is a bit of a fail­ing, because the res­ol­u­tion is very low and bad for a nor­mal camera.

I haven’t been able to start to work with it though. As it is designed to plug in to a phone dir­ectly the USB port is the wrong way round (male). I have ordered a USB cable which should fix this for me but it hasn’t arrived yet, expect­ing it on Monday.

The Panasonic Grid-Eye has also been delayed. The Panasonic staff mem­ber set me up with Braemac to arrange the details of the pur­chase. Unfor­tu­nately a full week has passed and Braemac hasn’t bothered to send me an email. If there isn’t any move­ment soon I’ll get them to line up Avnet instead.

Screen Invest­ig­a­tion

Find­ing a screen to go with my Banana Pi is prov­ing to be a bit messy, par­tic­u­larly a touch screen. It is look­ing like I will have to bond a screen, touch screen and pro­tect­ive layer. Very doable but a bit more work. I also have to decide on a screen size, the stand­ard ratios don’t gel well with the con­trol panel strip.


I have been look­ing in to elec­tric scales. They are essen­tially a strain gauge, a thin wire that is glued to the top of a metal block. As the block moves the wire is stretched and its res­ist­ance changes. The change is minor but with the wir­ing loop­ing a few times and a bit of amp­li­fic­a­tion… you have a set of scales.

The down side is that you have to have a metal block that moves up and down, which is bulky. To com­pensate for tem­per­at­ure and keep the accur­acy up the stand­ard load cell is an alu­minium block 5cm thick with a hole machined out of the middle to give it some flex. There are spe­cial thin designs, as used in nor­mal kit­chen scales, with reduced accur­acy and lifespan.

The biggest issue though is I need to get the weight con­cen­trated on a spe­cific point of the load cell. I am assum­ing put­ting the load cell in the microwave field wouldn’t work, so I have to trans­fer the load through the base of the microwave using small holes, then con­cen­trate it to a point. Another option is to have four sensors and bring the load down on four points. Either way I am prob­ably look­ing at a cus­tom piece of plastic to dis­trib­ute the weight. Cus­tom plastic = setup costs = unhap­pi­ness (and more research).

No Turntable

Another fea­ture I have been look­ing at is incor­por­at­ing a mode stir­rer which allows the turntable to be dis­posed of. A microwave forms stand­ing waves in the cham­ber, these pro­duce hot and cold spots in the food. The turntable is a really nice cheap trick to work around this prob­lem, by rotat­ing the food it hope­fully moves through a num­ber of hot and cold spots and roughly equals itself out. The mode stir­rer is another approach, basic­ally you put a fan in front of the microwave beam break­ing it up and spray­ing it around the cav­ity. This dis­rup­tion of the beam avoids the stand­ing wave, essen­tially you get lots of dif­fer­ent short lived wave pat­terns, and you shouldn’t get hold and cold spots. In prac­tice the dis­tri­bu­tion is more even but it isn’t con­clus­ive if it is bet­ter or worse than a turntable. The tech­nique has been around for a long time and seems to have come in and out of favour. The cur­rent mode stir­rer designs mar­ket them­selves as allow­ing a big­ger usable space in the microwave.

I am inter­ested in using the mode stir­rer because it makes other ele­ments of my life a bit easier. Not­ably the cam­era would work a lot bet­ter if the food you were look­ing at didn’t keep mov­ing. I could com­pensate for the move­ment in soft­ware, but avoid­ing the prob­lem seems easier. I also think the scales would be much harder to achieve with a turntable.

Unfor­tu­nately Alibaba (where I have sourced almost all my other parts) has let me down and nobody seems to sell them. The mode stir­rer is a thin metal com­pon­ent which would be fairly simple to make but must be done very pre­cisely. It is also a bit of fiddly RF design and as I have sworn off doing dark magic for lent it isn’t some­thing I really want to tackle myself. There are clearly people mak­ing them, I just might have to work a bit to find them.

As an inter­est­ing side note the cur­rent Panasonic designs with mode stir­rers have chosen to place the stir­rer in the bot­tom of the unit rather than the top, the his­tor­ic­ally stand­ard loc­a­tion. I’m not sure if this was motiv­ated by improved per­form­ance or cost, it does make the base feel oddly fat. Not some­thing I am look­ing to fol­low suit in either way, I am cur­rently pon­der­ing put­ting it in the side.

Other work

I also spent a con­sid­er­able period of time this week learn­ing about com­pan­ies, talk­ing to account­ants and read­ing excit­ing gov­ern­ment web­sites. Try­ing to fig­ure out if I start a com­pany now, play on as a sole trader and start a com­pany later or go with a com­pany & trust struc­ture. Cur­rently lean­ing towards delay­ing the com­pany found­ing but there are lots of little pros and cons to weigh up.

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