Modding a Keithley 197/How to print on front panels? - Page 1
Forum section: electronics / projects

author: Maxlor
author_rank: Frequent Contributor
timestamp: October 22, 2015, 11:00:51 pm
content: Today I got a "new" multimeter. And by "new", I mean it's 30 years old, but new to meIt's a Keithley 197. I've spent much of today going over it, smelling the parts, trying to figure out the most important chips, and reading what other people have said about it. Then an Idea struck me: Thanks to how the display part is implemented (separate board, connected to the main MCU via SPI, plus a few GPIO lines for 4 buttons) and the fact that full schematics for the meter plus full specs for the display controller are readily available, it's rather easy to replace the LCD with, say, an OLED display. And then, why stop there? If I have all the data going through an MCU under my control, I can add all sorts of features: statistics, graphing, serial interface for data logging, or data logging to internal memory with much more space, and downloading capability. Since I have quite a bit of vacation time coming up that I need to spend this year, but don't feel like travelling, I'm going to make this my christmas project.I figure I'm going to use a 256x64 res 3.2" or thereabout OLED, available from digikey or chinese suppliers. A PIC32MX to drive it. I'm going to keep all the original buttons since they interface directly with the meter's main MCU, and add separate buttons for the add-on functionality. I'd use the PICs internal memory to store measurements as they come in, and any serial interface would access only that.One thing I haven't quite figured out how to do is making the new front panel. I'm not going to modify the original front panel, I want to be able to back to stock. Having a new one made should be easy enough with a 3D printer or a laser cutting service like formulor or ponoko. But... how to actually put the labelling on there? I could have an acryllic panel engraved, but that'd be hard to read. Those laser cutting services don't seem to offer silk screen printing of the parts, hm. Maybe print it on photo paper then sandwich it in between two acryllic panels? Or trying to find some sticky foil that can be printed on, then cut it and put it on the front panel? I worry though that the edges in either case are going to look crappy.I've considered a 3D printed panel with paint-filled grooves, but there's quite a lot of small text that needs to go on the panel for the manual switches, I'm doubtful such paint grooves would look good enough in the end with small font sizes.Anyway, good ideas are welcome! Maybe you know of a laser cutting or 3D printing service that also does silk screens?

author: singapol
author_rank: Frequent Contributor
timestamp: October 23, 2015, 02:33:11 am
content: How about Casio label printer KL-60? It can use transparent tape as well as coloured ones.http://www.casio.com/products/Label_%26_Disk_Title_Printers/Label_Printers/KL-60L/

author: rikkitikkitavi
author_rank: Contributor
timestamp: October 23, 2015, 06:41:51 am
content: I would gonthat route too. A self adhesive sticker label, printed that you apply to the panel.Other option is to use laminated panel material. When you cut out the panel you engrave the panel to, and the different coulours of the laminate makes this visible.Dont have any suppliers at hand though.Ps let us know how this proceeds. I three 197/197A working. Damn fine pieces. All three are stable within 4,5 digits to a simple MAX6350 referrnce despite their age.

author: Thomas
author_rank: Regular Contributor
timestamp: October 23, 2015, 09:54:17 am
content: Sounds like a fun projectHow abouthttp://www.frontpanelexpress.com/.Probably expensive, but I think the result will be good.

author: Maxlor
author_rank: Frequent Contributor
timestamp: October 23, 2015, 01:00:28 pm
content: Quote from: Thomas on October 23, 2015, 09:54:17 amOh, thanks for that. There are a couple more services like that, schaeffer-ag.de (which seems to be partnered with frontpanelexpress) and panel-pool.com from BETA Layout (the pcb-pool people.) It looks like a printed aluminium front panel would come in at around €65, which isn't that cheap, but I might just go for it.Using a PCB as a front panel would only be slighly cheaper (maybe $50 from Elecrow), and look worse.

author: rastro
author_rank: Frequent Contributor
timestamp: October 23, 2015, 03:17:45 pm
content: Maxior,You may be interested in some prior work decoding and displaying the 197 signals to 7-segment LED's using arduino nano.https://www.eevblog.com/forum/projects/keithley-197-led-display-hack/msg493107/#msg493107The arduino code/sketch was posted as a text file because of post/attachment restrictions.Your project sounds much nicer.Good Luck and keep us posted...-rastro

author: Maxlor
author_rank: Frequent Contributor
timestamp: October 23, 2015, 04:27:07 pm
content: Yep, I came across your post already, and it certainly helped reaffirm the idea that this is doable and not terribly hard. I might use your code as a reference later on

author: Maxlor
author_rank: Frequent Contributor
timestamp: October 24, 2015, 09:55:24 pm
content: Today I sat down and took the measurements I need, the front panel with all the cutouts (I'll upload it once I figure out how to make inkscape use rounded corners on a polygon), and the digital transmission between MCU and the display board. I figure I'll document the gist here, in case anyone else wants to hack their 197.The pinout of the display connector is (standard CCW order, starting at the pin nearest to the rear right corner of the device):1 - C/!D2 - CLOCK (display clock, not SPI clock - you can ignore this if replacing the display board)3 - RESET4 - GND5 - VLCD16 - VLCD27 - VDD8 - dB (from Display board to MCU - goes HIGH when dB button is pressed)9 - REL (from Display board to MCU - goes HIGH when REL button is pressed)10 - STO (from Display board to MCU - goes HIGH when STO button is pressed)11 - RCL (from Display board to MCU - goes HIGH when RCL button is pressed)12 - SCK13 - MOSI14 - !CSData transmission happens over 3-wire SPI communication with an additional C/!D (command/!data) line. The SPI mode is 0 (CPOL = 0, CPHA = 0), i.e. CLK is low when inactive, data is latched on rising clock edge, and !CS is active low. Data is sent as 8 bits per byte, MSB first.The display controller is aNEC µPD7552, see that link for details. On startup, the MCU sends this sequence:MOSI C/!DComment0b 0001 0000 1Display Off0b 0010 0000 1Clear Data Memory0b 0011 0000 1Unsynchronized Transfer0b 0100 1010 1Mode Set:Div-by-3:1/3-bias:freq-div-1/2^90b 0000 0000 1Clear Blinking Data Memory0b 0001 0100 1Without Segment Decoder0b 0001 1000 1Blinking Off0b 0001 0001 1Display OnThis sequence configures the display for "Divide-by-3 time division" and disables the segment decoders. Afterwards, it sends the following sequence for every update. The commands are always the same, only the data bytes differ (those rows where C/!D is 0):0b 0011 0000 1Unsynchronized Transfer0b 0100 1010 1Mode Set:Div-by-3:1/3-bias:freq-div-1/2^90b 0000 0000 1Clear Blinking Data Memory0b 0001 0100 1Without Segment Decoder0b 0001 1000 1Blinking Off0b 0010 0000 1Clear Data Memory0b 0000 0000 00b 1110 1011 00b 1110 1011 00b 1110 1011 00b 1110 1011 00b 1110 1011 00b 1110 1011 00b 0000 0000 00b 0000 0000 0The display controller configuration never changes, so to get at the display contents, it suffices to intercept only the data bytes. The data bits control the following segments on the display (1 = on, 0 = off):AUTO,REL,STO,dB,AC,RCL,BAT,-6f,6e,,6a,6g,6d,6b,6c5f,5e,5dp,5a,5g,5d,5b,5c4f,4e,4dp,4a,4g,4d,4b,4c3f,3e,3dp,3a,3g,3d,3b,3c2f,2e,2dp,2a,2g,2d,2b,2c1f,1e,1dp,1a,1g,1d,1b,1cm(V),N,µ,V,k,m(A),,C,?,A,,,RMT,,Segments a, b, c, d, e, f, g are ordered in the standard order, i.e. a-f in clockwise order, starting with the topmost segment, and g being the one in the middle. Digit 6 is the leftmost one, digit 1 is the rightmost one. Note that the dp segment is on the left of the digit it belongs to.Below is a drawing of the display with all segments.

author: tooki
author_rank: Super Contributor
timestamp: November 01, 2015, 03:00:35 pm
content: Quote from: Maxlor on October 22, 2015, 11:00:51 pmI'm thinking that somewhere here in Switzerland, theremustbe a shop that has one of those inkjet printers that prints with UV-curable lacquer. Then it'd simply be an issue of having them print a PDF onto whatever substrate you've chosen. The result from these is actually quite nice.(As a funny aside, the only time I've ever seen one of those UV inkjets in person was years ago at theZurich "flagship" boutique of a promotional pen company, which somehow thought there was a viable retail business in selling individual personalized pens at around $12 a piece, for a pen worth maybe $1 without the printing, in one of the highest-rent shopping districts. They spent a fortune on custom shelving with electronics in it, and large tabletop touchscreens, but their software was gratuitously creative and thus hard to use, finicky, and then crashed when I tried to use it. Unsurprisingly the shop only lasted a year or so. Anyway, they had a Mimaki UV inkjet, one that could handle A2 size materials, outfitted with a tiny little jig to hold up to 6 pens at a time. A+ for effort, but yeah, I was amazed anyone gave that project a green light...)