With some luck the developers who has ordered and received a v0.1 AfreshBoard fully understood that this first version is experimental in its nature and that there are several different ways to use the circuit board. At the time the boards were manufactured there wasn’t any code for the AfreshBoard and most of the component values wasn’t even calculated. The correct way to use the board was to be decided on while writing the code and hopefully it was also clear that this would take some time.

The schematics that were published in the wiki are for the entire board and they were published by mistake, any board populated according to the schematic will be a bastard that will require special code. Consider the yet non-existent code written for the non-existent AfreshBoard v2.0;)

These are the instructions for assembling your AfreshBoard V0.1 in a way that makes it compatible with the non-existent AfreshBoard V0.2.

Issues:

1.

I somehow forgot that the Ri measurement pulse train will ‘rail’ IC2C’s output when the sensor is cold. This may overload the ADC3 limiting diodes in the Mega128.

I chose to fix this by fitting a series resistor called RHack between IC2C’s output and the Mega. A trace on the bottom of the board needs to be cut. RHack is a very simple and clean modification.

RHack

2.

The EGT circuit was designed in a hurry and I forgot that the offset voltage calibration must be highly stable and symmetric. The two pots R30 and R32 are now feed from V+ and V- and they aren’t that well regulated. Luckily the offset calibration is only fitted to be able to experiment with the standard part LM224 instead of the hard to get LT1882. As long as LT1882 is used the middle pad of the potentiometers can (and should) be connected directly to ground. As a side note the offset calibration was only fitted to be able to experiment with LM224.

Q: What’s up and down?

A: Locate the copyright text ‘(c) Jörgen Karlsson 2003. That is in the lower left corner of the board’s component layer.

The lowest components are best installed first. But on the other hand testing the board as you go along is makes it easier to find an error.

MCU:

First install the Mega 128, Pin1 is in the upper left corner of the Mega.

Fit MAX232, pin1 is in the upper right corner.

Fit 100n caps: C6,C9,C26. These are decoupling the Mega supply lines.

Fit 22p caps: C7,C8. These are for the oscillator.

Fit 1u caps (100n if MAX 202 or MAX232A is used.): C18, C11, C17,C15.

Fit R2 or a 1X2 female header strip where you fit R2.

Fit JP2, a 2X2 male header strip. But don’t fit the jumper itself until you need to use the second RS232 channel.

If you chose to play it safe it’s a good time to fit the ISP header. Loading the latest revision of the GenBoard/Firmware/BootLoader is probably a suitable test as that makes it possible to test the serial communication. Besides, the bootloader are pretty much the only available code for the AfreshBoard at the moment.

Filtered voltage output with external ground reference:

Fit IC5, a LM224/LM324 can be used here without any ill effects. Pin1 is in the upper left corner.

Fit 1M SMD resistors R16,R17,R36, R37.

Don’t fit R19, R20,C13,C14. Fit a 2X4 female header strip instead as the mentioned components are used to set the filter characteristics. You then make a filter module with a 2X4 male header strip and the filter components. That way it’s easy to configure the output filter.

Power supply:

Fit R6 and R12 (100k). They create a 2.5v potential.

Fit R55 and R56 (4.7k), These are used to measure battery voltage.

Fit R61 (4.7k), and D8. This is the VCC power indicator.

Fit C1, C2 (0.33u).

Fit DC1 ,the DC/DC converter. Pin1 is up.

Fit C23, C24.

If IC5 is used, fit C31 and C32. Don’t fit the decoupling caps for the other OPA’s yet.

Fit IC4, the 7805. Tab facing out.

Fit F1, the circuit breaker. You may jumper it if you use an external fuse.

Fit the transient suppressor diode C3 and the wrong polarity diode D1. Don’t fit D6.

Lambda section:

Fit IC2.

Fit R11 but don’t fit C4. C4 is for driving the heater in analogue mode and the code will most likely pulse the heater.

Fit R34 and R35. These are also for the heater.

Don’t fit R4 and R5; these are used for measuring the heater voltage when it’s used in analogue mode. Note that the lower pads of these resistors are the only ones connected to ADC1. A SMD jumper may fit here.

Don’t fit D4 and D5 (12v zeners), these are used to limit the maximum pump voltage and we will probably not need them.

Fit R3 (4.7k), this set the maximum pump current.

Fit R9 and R13, these set the amplification for the Nearst cell voltage.

Don’t fit R14, R15,C3, C5. This is used to remove the Ri measurement voltage from the Nearst signal. This is solved in software instead as this free up ADC0. This can be used as an emitter follower input, HP, LP or BP input to ADC0.

Fit T3 and T4 if you plan to use them. These are not related to the lambda circuit but they are best fitted before IC2’s decoupling caps.

Fit C27 and C28.

Fit T2 (TIP 120, 121 or similar Darlington NPN)

Jumper R1 with a wire. R1 is only there to make it possible to measure heater current (to find heater resistance).

EGT:

Fit IC1, this should be an LT1882 or LT1885 or similar part with extremely low offset voltage since the offset adjustment does not work.

Match and fit R21 and R24. (470k)

Match and fit R25 and R28. (470k)

Match and fit R22 and R23. (R21, R24 /100)

Match and fit R26 and R27. (R25, R28 /100)

Don’t fit R10, R33, R30, R32.

Connect the middle hole in the R30/R32 footprint to AGND.

Don’t fit R29, R30.

OffsetHack this is what you need to do if you need offset adjustment.

External EEPROM:

Don’t fit, this is replaced with multimedia card support.

External 8ch ADC:

Fit U$1.

Fit C16 (100n)

External high speed 12 Bit ADC:

Don’t fit unless you run custom ION code.

Jörgen Karlsson

Gothenburg, Sweden.