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July 9, 2009
Tutorial - Designing PCBs: SMD Footprints
I am a little in doubt about the pin numbers on the SMD pads. At the time you changed the tPlace layer color to white, those numbers changed in color too. Logical conclusion: The numbers are in that layer, and they will be printed on the bare copper pads, getting in the way of soldering ?!?
Is this okay? Is there some magic later in the pipeline that prevents the numbers from appearing? I see it happen in my own board too. Sometimes I had the numbers disappear when I hide the tPlace layer and sometimes not.
about 2 years ago
Thank you. But 2 lines further down he “gets rid of the decimal portion”. If a sign conversion of the decimal part is necessary, of course he will not bother to do it, but I want to keep the decimal part and am still unsure if I need to do a sign conversion or not.
But okay, looking again,
float tempcsb = (lsb>>4)/16.0;
float altitude = (float)( (msb << 8) | csb) + tempcsb;
tells me not to sign convert the altitude decimals, but just scale them and add them to the signed integral part.
From the datasheet:
The Altitude data is arranged as 20-bit 2’s complement value in meters. The data is stored as meters with the 16 bits of OUT_P_MSB and OUT_P_CSB and with fractions of a meter stored in bits 7-4 of OUT_P_LSB. Be aware that the fractional bits are not signed, therefore, they are not represented in 2’s complement.
Does somebody know how this is to be understood?
Should I take the fractional part (LSB/256 units) and add it to the signed integral part?
Or should I take the fractional part (LSB/256 units), multiply it by the sign of the integral part, then add the two?
I don’t have the part here so I cannot just try..
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