Modifying the 18Pin High Power Project Board

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devosbi

New Member
Hello all :)

I'm needing to modify the PICAXE 18 pin project board (High power version) to allow me to use a 12v supply to drive the H-Bridge.

I'm looking over the schematics and am aware of the changes from v2 to v3 to allow this kind of modification however I'm finding it bit hazy and am quite paranoid (Blown two PICAXE 18X's so far, don't want a third) about adding the seperate power supply, I'll be using a little 3 x AA battery box to power the PICAXE but i need to drive two gear-head motors with a 12v NiCad Battery, however the documentation states that a maximum of 6v is allowed, and i'm assuming that is because the power to the H-Bridge IC and the PICAXE is shared.

I'm assuming but not sure, there is a small resistor type thing (Single black band, I think its just a link) at the top near the programming jack, is it separating the power supplies the same way that the low power board with the darlingtons does? where you remove this resistor and the power supplies are isolated from each other.

I certainly don't want 12v channeling through my PICAXE and having to replace it again, so is anyone able to confirm this or inform me of the correct way to modify the board? (Again the instructions i found fairly difficult to understand)
 
hippy

hippy

Ex-Staff (retired)
Version V2 of the CHI035 was designed to have logic and motor power connected on-board and thus needs to have the board modified to work with higher than 6V ( See appendix D of CHI030.PDF ).

Which version of the board do you have ( see the text by FETs - will say ‘PIC Interface B V2’ or ‘V3’ ).
 
hippy

hippy

Ex-Staff (retired)
I don't have a CHI035 V3 board to check with but it looks like R9 joins V+ PIC and V+ PWR, and R9 is listed as 100R.

In principle, with V3 boards, all that is needed is to connect 0V/5V to the 0V PIC/V+ PIC and connect 0V/12V to 0V PWR/V+ PWR, separate V+ PIC from V+ PWR and it should work. Vs of the L293D should tolerate up to 36V.

I'm not sure where R9 is located but a continiuty check on V+ PIC / V+ PWR should identify it, as should its colour codings. The single black resistor is a zero-ohm link so possible not R9 ( an additional link in series with R9 or R9 has been changed to zero-ohm for V3 ), but page 2 of the manual does indicate cutting that to separate the power.

The best advice I can give at present is to continuity check V+ PIC, V+ PWR go to one or the other end of that black-band resistor, cut the resistor as per page 2 instructions, then continuity check V+ PIC and V+ PWR are indeed isolated before applying power.
 
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BCJKiwi

Senior Member
Yes on a V3 board, just remove R9

Note that on the V2 and V3 circuit diagrams, the location of R9 is different. The text on the CHI030/35 datasheet page 8 explains exactly what needs to be done to separate the supplies on the V2 board but neglects to say that R9 should be removed on the V3 board.

The datasheet is available from the help menu in the programming editor or by opening CHI030.pdf file in the datasheets folder within the programming editor folder
 
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devosbi

New Member
Thanks for the assistance, I tested with a multimeter just to be sure and it worked fine running the motors at 12v :)
 
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grimmjaw

Member
hi
this might sound stupid.a noob here...is the R9 resistor is the the resistor 100R with the single black band?to supply 9v to the ouput i should only cut the R9 resitor right?..just to make sure since this is last project board (2 have ady blown out)..my board is V3

thanks
 
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grimmjaw

Member
is the position is the same with 18 high power project board V3?
so even 6V can be connected the PIC eventhough from the datasheet said that the range is between 3V-5V..sorry for the lot of question
 
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westaust55

Moderator
Operating voltage for (nominal 5V) PICAXE chips

grimmjaw said:
is the position is the same with 18 high power project board V3?
so even 6V can be connected the PIC eventhough from the datasheet said that the range is between 3V-5V..sorry for the lot of question
Click to expand...
4.5Vdc and 5Vdc is in general promoted for the PICAXE chip range, unfortunately, many of the rev Ed datasheets do state 6Vdc.

For many of the PIC chips used for PICAXE, the absolute voltage is stated as 6.5Vdc, above which the chips is highly likely to fail (puff of smoke escapes). So 6V is getting rather close to the Absolute Max.

Microchip datasheets for the nominal 5Vdc PIC chips states the max normal continuous working voltage as 5.5V.

Accordingly, it is recommended that you limit the PICAXE supply voltage to 5Vdc.
 
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grimmjaw

Member
i see..that make sense..and i assume the possition of the R9 resistor in 18 pin project is the same with the 18 pin high power project board..thanks for the explainantion
 
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BCJKiwi

Senior Member
Check the rdatasheet/pages referenced in post #5

The circuit diagram is there. Trace the circuit if necessary to ensure you have R9 correctly identified.

After removing R9;
Supply the Picaxe with 4.5 from battery or 5V via a regulator.
Supply the high power circuit only from the 9v.
 
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