Analogue Calibration Board problem.

The bear

Senior Member
Hello Everyone,
Help required with my "Analogue Calibration Board" please. Link; PIC Analogue Calibration (75% off) ( (Out of stock).

The problem; It's loading the circuit under test (Picaxe light sensor 08M2 pin C.4).

With nothing connected to the Analogue Calibration Board, Using an ohm meter on the three connections; 0v to I/P = 1388 ohms & +5v to I/P = 853 ohms. It makes no difference which way the meter leads are connected.
The thread below is too clever for me:
Any suggestions appreciated.

Picaxe Analogue Calibration Board - replacement firmware
Picaxe Analogue Calibration Board - replacement firmware Thread starterAnobium Start dateApr 23, 2018



Senior Member
If you are wanting to replace the chip and use this firmware, you will need to compile the gcb code into hex, then program the new chip with a pickit2 programmer. If this is what you want to do then I can possibly help. Send me a PM.


Senior Member
Looking at the picture of the BAS810 board it looks like the I/P pin is connected directly to the microcontroller's ADC pin.
If this is true then the resistances you measure appear to be simply a feature of the ADC.

The forum is probably going to need you to give more details what you are trying to measure in order to be able to underdstand what your problem is.

What is the (Picaxe light sensor 08M2 pin C.4)?
What is the circuit that you are measuring?
What is the problem you see that is caused by it "loading the circuit under test"?

The bear

Senior Member
Thank for your responses.
@ Goeytex, It's kind of you to offer, but I'm just a simple bear. So a simple solution is in order. It's good to see you back on the forum. I wonder how
Tex is doing?
@Flenser, The setup consists of a dusk sensor to put the outside lights on. The sensor lives outside.
The loading I mentioned, daylight reading is around 130 ADC. When the ADC unit was connected the ADC dropped to 35 and stayed there regardless of outside luminance.



Senior Member
I have made a couple of garden lights switches (12v Lighting).

I used similar LDR's but to gnd & a 22k to +ve, using C.4 on an 08m2.
readadc C.4, b27
if b27 >= 150 then night
if b27 <= 130 then day

Switches a IRL520 FET with 150k pulldown on gate, connected to C.3 using 'pullup 8' to turn on FET at dusk.
C.1 & C.2 (SDA & SCL) connect to a DS3231 to turn off lights at midnight.


The bear

Senior Member
@ neiltechspec,
Mine is very similar, everything turns off at 11:00pm via a mains time-switch.
It has been working fine for several years, then the LDR started fading away, lights coming on too early.
Fitted the new LDR, code " if ADC < 35 then, get them lights on", or words to that effect.


Senior Member
The problem I found with the LDR's (happened twice after about 12 months), is they are not damp proof.
On inspection, failed ones were all corroded.

Solution - mount the unit inside the garage, sensor stuck onto inside of the window.
Not failed since (about 3 years now).



Senior Member
The problem I found with the LDR's (happened twice after about 12 months), is they are not damp proof.
On inspection, failed ones were all corroded.
I have created two dusk switches using solar garden lights. They are cheap to buy. While they tend not to last very long as garden lights (In my experience, the NiCd cells are pretty poor quality), the solar cells are usually well protected from the weather in their stainless steel enclosure. I wire the solar cell directly to the PICAXE's ADC input.


Senior Member

My suggestions are:
I would first test the calibration board seperately from your 08M2 light sensor circuit with something like this:

I don't own a calibration board but with a resistor divider like this I would expect you to be able to read values from near 255 down to around 127/128. Then switch the two resistors around to test from around 127/128 down to near 0.

The resistor values don't have to be this high, you can use smaller ones..

Once you know whether your calibration board is working as expected I would then try using this circuit shown on page 29 in the PICAXE manual #3 to see what range of values you get reported on the calibration board between bright light and darkness:

I don't know what your problem might be using the calibration board on the circuit in your 08M2 light sensor board.

You only show the on connection for the I/F so I want to confirm that you have actually connected all three GND, I/F and Vsupply from the light sensor to the calibration board?

I don't recognize the circuit that you use to connect the LDR to the 08M2 ADC pin and I don't understand how it works. Can you tell us where you got this circuit?

Last edited:


Senior Member

I don't think the BAS810 board was ever intended to make in circuit measurements, and also it was considered Obsolete and/or Unnecessary by Hippy and Technical 16 years ago ! There, Technical wrote: "As Hippy suggests, it is totally unnecessary for the PICAXE system as you can get instant readings using a quick debug test program : ." ;)

As for LDRs, their prime advantage is that they have a Logarithmic characteristic so are ideal for photographic metering. But for simple light threshold detection, then one of the many silicon-diode-based devices : Photo- Diode, Transistor or PV panel, etc., can be used in either "reverse leakage" (current) or forward "voltage-generation" modes. But note that the light level is proportional to the forward (or reverse) current, so a shunt resistor needs to be used to make a reliable voltage measurement (the open-circuit forward voltage is a better indicator of the temperature of the diode ! ). However, for wide-range measurements a "current-to-frequency" conversion is generally the best method, for example using a PICaxe's internal comparator (or I've even considered the "touch" oscillator hardware). Thus, I achieved a continuous range of around 5 decades (i.e. 1 Hz to 100 kHz), corresponding to direct sunlight down to almost moonlight. ;)

Cheers, Alan.

The bear

Senior Member
Hi everyone,
The bear is receiving, thanks to all for your suggestions.

Flenser, will try your circuit.
AlleyCat, Interesting re; hippys remarks.

I have found the BAS810 board very useful, it's not always easy to debug (Remote) established projects.

It has been known, for me to construct a duplicate circuit to bench test.