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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