Slow text input in html field from barcode scanner

Question

I have a webpage in my LAN in order to input barcodes in real time to a db through a field (framework django + postgresql + nginx). It works fine, but lately we have a customer that uses 72 char barcodes (Code Matrix) that slows down inputs because before next scan, user must wait the redraw of the last one in the field (it takes about 1-2 seconds, redrawing one char after the other).

Is there a way to reduce latency of drawing scanned text in the html field? Best thing would be to show directly all the scanned barcode, not one char after the other. The scanner is set to add an "Enter" after the scanned text.

Answer 1

At the end, as Brad stated, the problem is more related to scanner's settings (USB in HID mode), although PC speed is also an issue. After several tests, on a dual core linux machine I estimate delay due 85% to the scanner and 15% to PC/browser combo.

To solve the problem I first searched and downloaded the complete manual of our 2D barcode scanner (306 pages), then I focused on USB Keystroke Delay as a cause, but default setting was already set to 'No Delay'.

The setting that affected reading speed was USB Polling Interval, an option that applies only to the USB HID Keyboard Emulation Device.

The polling interval determines the rate at which data can be sent between the scanner and the host computer. A lower number indicates a faster data rate: default was 8ms, wich I lowered to 3ms without problems. Lower rates weren't any faster, probably because it was reached the treshold where PC becomes the bottleneck.

CAUTION: Ensure your host machine can handle the selected data rate, selecting a data rate that is too fast for your host machine may result in lost data: in my case when I lowered polling interval to 1ms there were no data loss within the working PC, but when testing inside a virtual machine there was data loss as soon as I reached 6ms.

Another interesting thing is that browsers tend to respond significantly slower after a long period of use with many tabs open (a couple of hours in my case), probably due to caching.

Tests done with Firefox and Chromium browsers on old dual core PC with OS Lubuntu (linux).

Answer 2

This probably has nothing to do with your page, but with the speed of the scanner interface. Most of those scanners intentionally rate-limit their input so as not to fill the computer's buffer, avoiding characters getting dropped. Think about this... when you copy/paste text, it doesn't take a long time to redraw characters. Everything appears instantly.

Most of those scanners are configurable. Check to see if there is an option on your scanner to increase its character rate.