Cheap Idea for a DRO

[BillTodd]

I have had a quick look at your circuit (not your code yet). I use that size PIC a lot so I have lots in DIP and surface mount. With the way you drive the reader board do you not get problems with the grounds as the reader +1.5V is grounded to the SS metal parts of the caliper. I guess the PC 0V on the com port should not come into contact with your mill/lathe machine ground?

If you look at the multi-scale reader, I use an external PSU (wall-wart) to power the reader and off-set the supply to +3v5 and -1v5, so that the PC and scale grounds can be connected together.


My code handles both BCD and Binary scales automatically by measuring the clock pulses at switch on. It passes the scale data to the PC in string form, the PC/VB app determines which format and unit the data is in, then converts it to Inches (which is the inherit unit of the binary scales). Objects within the app convert the unit as required. I find that displaying MM and Inch (decimal and fractions) simultaneously is VERY useful.

If you're planning a display device make sure it's got an X2 (for lathe use) and a reverse button (easy swithing from absolute and relative is also very handy).

[1113562]

If you look at the multi-scale reader, I use an external PSU (wall-wart) to power the reader and off-set the supply to +3v5 and -1v5, so that the PC and scale grounds can be connected together.


My code handles both BCD and Binary scales automatically by measuring the clock pulses at switch on. It passes the scale data to the PC in string form, the PC/VB app determines which format and unit the data is in, then converts it to Inches (which is the inherit unit of the binary scales). Objects within the app convert the unit as required. I find that displaying MM and Inch (decimal and fractions) simultaneously is VERY useful.

If you're planning a display device make sure it's got an X2 (for lathe use) and a reverse button (easy swithing from absolute and relative is also very handy).

Hi Bill,

Thanks for this. I obviously did not look too hard at your diagrams did I?

The web site has been up and down over the past few days and I kind of gave up last night. I'll try to get a bit more time on it looking at your stuff.

I like the idea of using a PC or laptop for the readout's and controls. I've never really got into VB programming but I'm quite happy with PIC assembler (not C though...that scares me). I was told that VB interface to RS232 Com Port is not that well documented and is a bit tricky? Have you thought of a USB version seeing that RS232 com ports seem to be disspearing off the modern PC's (especially laptops)?

Did you have any thoughts on producing longer bar's/PCB for the read head to slide on? All the cheap Chinese calipers seem to come with a short 150 mm bar.