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--- ea-ps_2084-03b [2015/05/27 05:31] – [acquisition] kingkevin
+++ ea-ps_2084-03b [2015/05/27 18:45] – [mutli-meter] kingkevin
@@ Line 53: / Line 53: @@
 It will set the voltage and current which are set, actual (measured by the power supply), and [[#mutli-meter|measured]] (measured by the DMM)
-===== mutli-meter =====
+===== multi-meter =====
+To measure the output of the power supply I used two [[http://uni-trend.com/UT61E.html|UNI-T UT61E]].
+These are good multimeters for electronics which you can get [[http://www.aliexpress.com/wholesale?catId=0&SearchText=uni-t+ut61e|quite cheap]], with 22000 counts, and offer connection to the PC.
+More functions and its accuracy are available in the [[http://uni-trend.com/manual2/UT61English.pdf|manual]] ({{:ea-ps_2084-03b:ut61english.pdf|archive}}).
+==== connection ====
+The DMM comes with an RS232 [[http://www.uni-trend.com/en/product/2014_0626_553.html|UT-D02]] cable.
+To connect to the PC you need a RS232 to USB converter (are PCs with COM ports still manufactured?).
+The cheapest RS232 to USB converter one is based on the CH341 chip.
+Sadly the 7O1 mode used by the multimeter [[http://www.cnx-software.com/2015/03/07/sigrok-and-pulseview-in-ubuntu-14-04-with-uni-t-ut61e-digital-multimeter/|isn't supported]] by the linux driver.
+I also tried the [[https://github.com/karlp/linux/tree/ch341-3.18.6|patch]], and after toggling DTR I get wrong data out.
+I also has an old ARL3116 based RS232 to USB converter, but there too the mode didn't seem to be supported.
+Finally I found a FT232-based RS232 to USB converter.
+This is an expensive cable (but good quality), from an evil company, and it worked.
+But instead of using it, I decided to connect the cable to a CP2102-based UART to USB converter.
+Then you have to keep two things in mind:
+  * RS232 signals are between -12 to +12 V, while UART uses 0-5 V. This was solved by simply using the 5 V pin from the converter to power the cable.
+  * RS232 signals are inverted compared to UART. This was solved by inverting the signal using an NPN transistor and two resistors.
+More details about the cable and modification is described in this picture: