Let's Make Robots!

new project: solar rover based on Picaxe 18X

the idea is to use a picaxe 18X as a brain for a little solar rover.

i have discovered that a picaxe can function as a solar angine because it works down to 2.5 volt

so im planning to use a solarbotic 33x37 policristalline cell wich provide 6.3V - 30ma

picaxe remain in nap mode untill caps reach a voltage near to 3.5 v then activate motors to accomplish an action loop....

and so on....

i use a 74ac240 as motor drivers and geared pager motors ...


by the test i have done till now it seems all can work properly....




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Since you are using the LDR in a voltage divider, you should first measure the resistance of the LDR (outside of the circuit) in the light and in the dark to get the range.

The output at the middle of the divider (where the ADC is reading) is  Vout x (4700/(R+4700)) where R is the resistance of the LDR.

Then the PICAXE ADC will convert that volatage to an 8 bit value. 

Do the math.  

I wouldn't be surprised if it were 1 meg ohm.


 PS. On any solar project, you need to minimize energy use. Zeners are notorius power hogs (relatively speaking)

how to drop the clock speed to 32kHz ?

how to  turn off the BOD?

 i ma testing too, it's incredible the fitness of picaxe in lo-voltage, solarized  setup

it's able to blink a led with panels in deep shadows :O

thanx for the tips....

i am using picaxe 18x

have this micro a BOD onboard?

i use external circuitry to detect the brown out

it's a simple resistor and zener 2.7v connected to ADC in

i have discovered that the adc reading is related to Vcc so i can easily detect when the voltage reach a certain threshold with adeguate precision

all works fine on breadboard

motor can work at full power for 50 ms relying on cap energy

this time is sufficient to move the weight of the bot


those are the geared pager motors



the cap is 4400 uF

Would you use the brownout detection te send the micro controller to sleep? Or would you just disable the detection?

The Brown Out Detector merely triggers a reset if the voltage gets below the setpoint. The PICAXE can actually run at a lower voltage, but you have to monitor it carefully.

Turning off the BOD aloow the PICAXE to keep running at a lower voltage, but you also have to consider the effect on the other components on the bot.

It may sound great to run at 2 volts, but considering a motor driver will drop at least 1.2 volts then your motor would actually "see" only 0.8 volts.

The most efficient way to solarize a PICAXE is:

1. turn off the BOD, drop the clock speed to 32kHz

2. drop the clock speed to 32kHz

3. Pull down all unused inputs (100K resistor is fine)

4. turn off any unused ADC inouts

5. use spare pins to power sensors and turn off when not being used.

6. mimimize LED current. Newer Blue LEDs will be visible with a 100K resistor

7. monitor voltage  

8. use NAP or SLEEP mode as much as possible. Wake up from NAP mode, check voltage if OK then run; otherwise back to sleep mode.


NAP period


read picaxe_manual2.pdf 





some thoughts:

You can seriously lower the PICAXE power consumption by slowing down the clock speed. Thereby using microamps instead of millialmps. Combined with NAP, you can improve the performance of solar powered bots.

The milliamp ratingof the solar cells  is for full direct sunlight only. It falls off drastically in room light. You may only get 1 or 2 milliamps inside.

If you are using a capacitor for power storage, you can use one ADC pin to check the voltage level to see if there enough power to run.

Watch your energy budget.  

What motors are you using? Most motors will have a current spike, many times it running rating, to get started and overcome inertia.

Solarizing projects is a definite challenge, but a lot fo fun!

Myc Holmes 




I am sorry to steal, but using the Picaxe how do you invoke "nap mode"?
Keep us posted. I'm planning on eventually doing the same with my solarbotics cells, so hopefully I can learn from you ...