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This page describes the 1 MegaByte logger upgrade that has been available for all 2A0 pre-built units and DIY kits since late August 2005. It increases 2A0's on-board logging capacity by 32 times. Logging times to tens of minutes, at the fastest logging rate, are now possible. 2A0 units with this addition are known as the 2A1.

Brief History : 2A0 was originally released with no on-board logging memory, but it had provision for up to 32 kBytes. With the Rev-3 2A0 PCB, the optional 32 k on-board logging memory was made standard and supplied with both DIY and pre-built units.

Memory upgrade : involves modifications to existing 2A0 units, including removal of the current 32 kbyte TWI EE memory for 1 Mbyte SPI EE memory. A processor upgrade is also made to cater for the increased code needed to drive the extra memory. All 2A0 units can be modified and the parts to do this are available as a DIY upgrade kit. Electronic construction skills are involved in making the upgrade but should be easy if you built your own 2A0 unit. Tech Edge can make the changes for you if you purchased a pre-built unit.

Buy the 2A1 logging module or upgrade kit

On-Board Logging Overview

Logging is controlled by a single switch on the top of the 2A0 case. User feedback for on-board logging is provided by WBo2's red LED (which also provides general-status feedback). More information on how logging works can be found on the detailed WBo2 Logging Information page.

2A0 Circuit Details & Changes Required

If you're going to make the changes yourself then here's how it's done. Remember that Tech Edge can make the changes for you, for a small fee, if you prefer. We may be able to advise of people in your local area who can also do this. All red links below are to pop-up images, but you need JavaScript enabled for this feature. Alternatively, go here for all the images in one place.

The original 2A0 on-board logging circuit, with 32 kbyte EE memory using TWI (Two Wire Interface, but also know as the Philips I2C bus), is shown at far right. Full schematics are available here so we have just shown the important sections and changes required. Basically the processor's TWI control pins (27 & 28) are now used to control an SPI interfaced chip, and an unused MUX input X1 is used to sense the new logger control-button. The processor SPI signals MOSI, MISO & SCK are already available on the Y5 connector, but two Y5 pins (10 & 12) must be freed up for the old TWI signals. Note that Y5 pin 11 was originally unassigned and is available for use. Here's what you have to do :

  1. Take off the existing logger button PB1. You can also take off the post the logger button is attached to. The logger button is not used again. There is no logger button on the Rev-2 PCB.

  2. Take out 28 pin U1 (lever a screwdriver off the end plate to avoid damaging the 15k resistor) and store it.

  3. Take out 8 pin U2 and store it.

  4. Take out the four screws securing the PCB to the case.

  5. Remove the two 2k2 5% resistors R301 & R302 (red, red, red) located just above the processor as shown in the image. We suggest you cut the old parts rather than risk damaging the PCB. You can heat the remaining parts of component leads, one at a time, and tap the board on the bench to remove them.

  6. Remove capacitor C311. Again, we suggest you cut its leads. There is no C311 on the Rev-2 PCB.

  7. Remove 22k 5% resistor R303 (red, red, orange), noting that R303 is between the processor and the Y5 "rescue-reflash" header pins. This image shows the 22k resistor. There is no R303 on the Rev-2 PCB.

  8. On the component side, cut the heavy trace between Y5 pins 9 & 10 (this isolates pin 10 from 12 Volts). The previous image shows this also.

  9. On the solder side, cut the trace from Y5 pin 12 before it gets to the through-hole via (this isolates pin 12 from processor RESET). The red box shows this, but note the cut is obscured by the red wire that is added later.

  10. This step is quite difficult. On the solder side isolate U3 pin 11 from the 3 GND connection points. U3p11 is the 3rd pin of U3 away from Y5 and is indicated by This is indicated by the yellow box. Carefully measure that resistance between U3-p11 & the surrounding copper to ensure it is not connected by any fine shards of cut copper.

  11. Another tricky operation is to swap two resistors, from the top of the PCB to the bottom, to make room for the memory module. remove the 47k R406 (yellow, purple, orange) and 1k5 R1 (brown, blue. red) resistors on the other side Y6. Rather than trying to do keep the resistors, we have supplied replacements, so cut the old ones out and remove the pins, and use the new resistors (47k is closest to the LEDs) remembering to put them on the SOLDER side of the PCB this time as shown here (also shows 3 wires added later).

  12. Insert (from the component side) the 9 pin header strip making sure the pins are vertical. You may consider resoldering the existing 3 pins in positions 1-2-3 so they are all vertical. Now solder the 9 pins and check that all 12 pins now align and are vertical.

  13. The three wires you noted above must now be soldered. Begin by soldering X1 to Y5, which is the light blue wire from U3p11 to Y5p10.

  14. Solder two EE memory control lines from U1 to header pins Y5. First is SST EN to Y5 or U1 pin 27 to Y5 pin 11 (black wire). Then solder SST HO to Y5 which is U1 pin 28 to Y5 pin 12 (red wire) shown here.

  15. When all soldering is complete the new Atmel Mega168 processor U1 can be inserted. You may have to first bend the chip's leads at a sharper angle before it can be placed in the socket. Remember that the end with the dimple should be to the left as was the old Atmel Mega-8 processor.

  16. The logger module can now be inserted. This is shown here.

At left is the schematic of the modified 2A0. Click on the image to see the logger module's schematic.

One major task remains, drilling the holes for the module's press-button and 3 mm LED. This is made easier as the case has an accurate grid that can be used to mark the hole centres. Take care to do this as a miscalculation here can make a mess of the case. We recommend you use a drill press for best accuracy, and feed the drill very slowly. The ABS plastic tends to grab when using a general purpose drill bit so make sure you firmly hold down the case, and drill from inside (the side shown).

Hole dimensions are shown at right (enlarge). Note that both new holes have centres 2 mm to the right of the indicated grid line. The larger press-button 4 mm hole (5/32") is just off the grid line, towards the smaller hole, by 0.5 mm. The smaller 3.2 mm hole is 9.0 mm from the grid line.

As a reminder of the finihed product's appearance, click on the image at left to enlarge.

You may find that the hole you drilled for the button may need some filing or enlarging to get the button to operate freely. Make sure you check the fit of the holes etc. with the main PCB screwed down as the PCM can move around a little under the 4 screws.

Kit Parts & Module Details

At left is what you get in the 2A0->2A1 upgrade kit. Click to enlarge x2. The actual parts list is described in the next section.

The purpose of the label is to cover up the hole that would be left when the logger button is relocated.

At right is the layout of the logger module itself. Not shown is the logger button, and the 3 mm red LED. To see an enlarged version of the module click here or the image. Or for the module's schematic,

Parts List - some part numbers are as per existing parts

1 2A-1ML       pre-built & tested 1 Mbyte logger module for 2A0 ("Megabyte Logger")
1 Y5 12 pin header (maybe 3 spare pins for some installations)
1 U1 Mega-168 preprogrammed processor
1 R1 1k5 5% resistor - replaces original R1 possibly damaged
1 R406 47k 5% resistor - replaces original R406 possibly damaged
1 red wire 55 mm long "wire wrap" wire
1 black wire 55 mm long "wire wrap" wire
1 blue wire 15 mm long "wire wrap" wire
1 label te Wideband label covers existing logger button hole