I pulled out the service manual and located the serial port circuitry. Below is an excerpt of just that section. You can see the infrared LED, H1201, is directly driven, through a 261\u03a9 resistor, from the TXD pin on the main controller. Thus, I should be able to pull the signal from the \"far side\" of R1201. The location of that resistor is pointed out in the image.<\/p>\n\n\n\n Placing a probe on the resistor, I was able to verify with my multimeter that it was a 5V signal and that it did swing around when I hit the print button on the scope. Since I was still waiting on my USB-to-TTL Serial converter to arrive though, I had to find a different way to capture the signal.<\/p>\n\n\n\n Enter, Arduino.<\/em><\/p>\n\n\n\n I rigged up an extremely simple program that sets up a software serial port on one pin, reads from it, then outputs the data over the USB serial port back to the PC.<\/p>\n\n\n With that running on the board, I attached a probe from pin 4 to that resistor on the scope board. Luckily, lots of other test equipment outputs in this format and someone has had the misfortune of already needing a translator \u2014 the Netpbm project has a program called thinkjettopbm<\/a> that will convert that raw stream into a PBM image which can then be converted to PNG with pnmtopng<\/a>.<\/p>\n\n\n\n Voila!<\/p>\n\n\n\n While waiting for parts to arrive to build a proper optical serial interface, I really wanted to get some screenshots off of my oscilloscope. Knowing that the infrared LED in the interface is directly transmitting the serial signal, I figured I should be able to tap into that driving signal to obtain the serial information.<\/p>\n","protected":false},"author":1,"featured_media":417,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[3],"tags":[71,69,39,72],"class_list":["post-416","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-hardware","tag-arduino","tag-fluke","tag-hack","tag-serial"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"https:\/\/areciv.com\/blog\/wp-content\/uploads\/2013\/02\/circ.png","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/areciv.com\/blog\/wp-json\/wp\/v2\/posts\/416","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/areciv.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/areciv.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/areciv.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/areciv.com\/blog\/wp-json\/wp\/v2\/comments?post=416"}],"version-history":[{"count":11,"href":"https:\/\/areciv.com\/blog\/wp-json\/wp\/v2\/posts\/416\/revisions"}],"predecessor-version":[{"id":4436,"href":"https:\/\/areciv.com\/blog\/wp-json\/wp\/v2\/posts\/416\/revisions\/4436"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/areciv.com\/blog\/wp-json\/wp\/v2\/media\/417"}],"wp:attachment":[{"href":"https:\/\/areciv.com\/blog\/wp-json\/wp\/v2\/media?parent=416"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/areciv.com\/blog\/wp-json\/wp\/v2\/categories?post=416"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/areciv.com\/blog\/wp-json\/wp\/v2\/tags?post=416"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}![\"\"](\"https:\/\/areciv.com\/blog\/wp-content\/uploads\/2013\/02\/circ.png\")
<\/figure><\/li>![\"\"](\"https:\/\/areciv.com\/blog\/wp-content\/uploads\/2013\/02\/WP_20130211_008.jpg\")
<\/figure><\/li><\/ul><\/figure>\n\n\n\n\n#include <SoftwareSerial.h>;\n\nSoftwareSerial fluke(4, 13);\n\nvoid setup() {\n\tfluke.begin(9600);\n\tSerial.begin(9600);\n}\n\nvoid loop() {\n\tint tmp = fluke.read();\n\tif (tmp > -1) {\n\t\tSerial.write((uint8_t)tmp);\n\t}\n}\n<\/pre><\/div>\n\n\n
I configured the scope for ThinkJet format and 9600 bps under the \"Special Funct\" menu, then hit \"Start Print\". I used CoolTerm<\/a> to capture the stream to a file, which left me with a raw stream of data meant to be interpreted by a printer as old as me<\/a>…<\/p>\n\n\n\n![\"Oscilloscope](\"https:\/\/areciv.com\/blog\/wp-content\/uploads\/2013\/02\/monitor-12v-noisy-300x300.png\")
<\/figure><\/li><\/ul><\/figure>\n","protected":false},"excerpt":{"rendered":"