rocketnumbernine

Andrew's Project Blog: Hardware, Software, Stuff I find Interesting

level converter pcb

The Level converter PCB has finally arrived from BatchPCB. Their service was easy to use and took about 4 weeks to arrive (as advertised).

Because the board was less than the minimum 1" square they had already doubled it up so I got 2 for $2.50 + $1.20 postage (untracked and uninsured) and $10 handling. With this size the service obviously dwarfs the PCB cost so its worth batching up your order to reduce the overhead. I had ordered two of the level converter board and another very small SOIC-8 break out board and received 8 pieces for $21.20.

I was keen to use this to test SMT soldering in my converted mini oven. Adding paste using a syringe was much harder than anticipated. The paste was fairly thick and left thin tails which required cleaning up. bi-directional level converter boardDespite dozens of tests with the temperature gauge on the oven, half way through the process it stopped working so I had to play it by ear - I turned the oven off just after the solder went molten and reflowed around the components (a magical sight). I might have left it a little late as the PCB has a slight brown tint to it.

bi-directional level converter board

The excess solder that hadn't been cleaned off the board had formed small balls which could be chipped off as can be seen below. The pads which had too much paste formed balls around the pins of the chip. Otherwise the solder flowed around the components surprisingly well.

bi-directional level converter board closeupI had made two screw ups with the PCB layout: first the the labels are too small to read, secondly more serious I mixed up the pin layout on the MCP1700 LDO, which resulted in it burning out when connected to 5V - luckily without harming any other components.

Fixed PCBIt was just about possible to replace the burnt out component with a T0-92 version soldered to the capacitor pads. This worked fine and the power shift and logic level converter worked as expected. I need to test the max amount of current that the LDO 5V-3.3V downshifter can provide without getting too hot (the T0-92 package is likely to be better than the SOT-23 anyway).

TI TXS0104E and family

Another option in level conversion is the Texas Instruments TXS0104E and family these are available in 2-8 bit conversion packages in both open-drain and push pull versions. These chips also have a output enable pin which can be used to pu the I/O pins into tri-state mode which could be useful.

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Tags/Categories: projects, shifter, voltage conversion, 3.3V, 5V, regulator, LDO, MOSFET, MCP1700