Adjusting SVout Offset for LD01

LD01 and Logged data show different AFRs

Note: Tech Edge has not made available the LD01 for several years. We provide this information for those people who still have these reliable units and want to get the most out of them

For various reasons the LD01 may not see the same voltage that WBo2 thinks it is producing. This results in the AFR displayed on the LD01 being a little different to the more accurate IPx value that is available from the RS232 data stream (ie. the RS232 data frame contains the exact Ipx value at any given instant).

Note : newer digitally connected displays like the LA1 and LD02 do not suffer this problem.

The LD01 display reads the SVout voltage then interprets and displays it as an AFR. The SVout signal (this is the same as the version 1.5's Vout signal) is produced by WBo2's 10 bit PWM hardware and is filtered and buffered before being sent to LD01. The raw 10 bit SVout value comes from a 65 word lookup table and is generated from an internal variable called Ipx. Ipx is directly related to the Lambda (or AFR).

WBo2 firmware's (we recommend you obtain the latest firmware) has an EEPROM configuration value called SVout_offset at offset 0x37. This config value is normally set to 00 and changing it will effectively move the SVout table richer or leaner. You get richer offsets by providing a negative number as shown in the table to the right. Using a positive number adjusts the display leaner.

  • -2 = 0xfe
  • -1 = 0xff
  •  0 = 0
  •  1 = 0x01

Use the WButil terminal program to change the Svout offset as follows: First set the COM port and then enter these commands - the text at the right is just a comment :

At this point the LD01 display should read, ideally, 14.7. If the display reads less than 14.7, then issue commands :

until you see the display just showing 14.7 (it may flicker 14.6 then 14.7 .... and record the xx hex value. Now increase xx until the display flickers 14.7/14.8 and record the yy from the p02yy you just entered. Get the average of xx and yy (eg. xx=0a, yy=0c, average = 0b) and call this zz. This average (zz) is the config SVout_offset value you must place in EEPROM at location 0x37 as follows :

If you found the display reading greater than 14.7 then the xx and yy values you enter will be negative in the range of ff -> 80 although realistically you are unlikely to have to put in a value less than f0.

Lastly, check the displayed value against the logged value - perhaps some tweaking of the above procedure will be necessary.

Also, when/if you upgrade the WBo2's firmware, you may have to save the above calculated value and set it up again (although an new/updated flash program should give you the option of retaining any parameters you have set up before it reflashes).