Pebbles >>> 28x2 >>> Regulated Supply

slimplynth

slimplynth

Senior Member
After owning a 28X2 3v for some months, was forced to crack it open last night.. couldn't put my hands on the 5V version; also as I've never had to power anything at 3V I thought best to have a go.

Have tested and the circuit gives a steady 1.89V supply to the 28X2 which is close to the lower limit stated in Manual 1 - as low as 1.8V

The Regulator is an LM317T - I'm not sure what this setup is going to be used for... but it's likely the 28X2 will be configured to output to as many 4066's as I can breadboard (just bought a big 'un)

From the Pebble below, Is there a problem with using a 100uf capacitor to ground? it was the lowest value I could put in last night..

...I guess basically what I'm asking is, "Would you be happy to breadboard your one and only 3V-28X2 like this? If not, what would you change?"

Cheers

Edit: Amended pebble below as per Westaust & BB's posts...

Code: 
Wire||74|44|21||11|#FF0000|3|11||10|
Wire||47|17|21||11|#000000|16|11||10|
Wire||74|209|21||11|#FF0000|3|11||10|
Resistor|1000|105|339|1|Resistor|R?||3||IC||
Wire||130|363|12||11|#FF9900|3|11||10|
Wire||76|180|11||11|#FF0000|4|11||10|
Capacitor|1K63: 100nf|185|142|1|Capacitor|C?||3|1|||cap_131
Wire||290|17|21||11|#000000|3|11||10|
Wire||317|402|21||11|#000000|2|11||10|
Capacitor|100uf|109|404|2|Capacitor|C?||2|3|||cap_322
Note||82|252|1||||1||1 - LM317T||NOTEPAD_11
Note||108|284|1||||1||2 - LM317T||NOTEPAD_11
Note||137|311|1||||1||3 - LM317T||NOTEPAD_11
IC||471|210|2|28X2 - 3V - PIC 18F25K20|U?|||DIP28|IC||DIP28_2
Wire||586|402|21||11|#000000|2|11||10|
Wire||613|402|21||11|#FF9900|3|11||10|
Wire||640|17|21||11|#000000|3|11||10|
Resistor|10000|213|311|1|Resistor|R?||3||IC||
Wire||91|374|22||11|#00A060|4|11||10|
Capacitor|100nF|589|335|3|Capacitor|C?||1|4|||cap_413
Wire||158|374|23||11|#000000|3|11||10|
BREADBOARDSTYLE=BB12
SHOWTHETOPAREA=false
 

Attachments

Last edited:
hippy

hippy

Technical Support
Staff member
Genrally a schematic is what people can quickly answer on, but failing that, a screen shot of the breadboard layout will help those who haven't got PEBBLE installed.

The 28X2-3V should work okay from 2 x AA or 2 x AAA batteries so that may be the easiest way to start.
 
W

westaust55

Moderator
I frequently use a larger electro than shown on the datasheets.
Don't see any problem with your proposed voltage reg circuit.

Note on datsheet states:
†Optional—improves transient response. Output capacitors in the range
of 1μF to 1000μF of aluminum or tantalum electrolytic are commonly used
to provide improved output impedance and rejection of transients.
Click to expand...
Also consider a 100pF ceramic across the PICAXE supply pins.

Also need an extra wire (green in the pics) to get the +3V to the PICAXE chip. See below

Code: 
Wire||74|44|21||11|#FF0000|3|11||10|
Wire||47|17|21||11|#000000|16|11||10|
Wire||74|209|21||11|#FF0000|3|11||10|
Resistor|1000|105|366|1|Resistor|R?||3||IC||
Wire||130|345|11||11|#FF9900|3|11||10|
Wire||76|180|11||11|#FF0000|4|11||10|
Capacitor|1K63: 100f|185|142|1|Capacitor|C?||2|1|||cap_121
Wire||263|17|21||11|#000000|3|11||10|
Wire||103|400|11||11|#FF9900|6|11||10|
Wire||371|402|21||11|#000000|2|11||10|
Capacitor|100uf|109|404|2|Capacitor|C?||2|3|||cap_322
Note||86|281|1||||1||1 - LM317T||NOTEPAD_11
Note||112|308|1||||1||2 - LM317T||NOTEPAD_11
Note||56|335|2||||1||3 - LM317T||NOTEPAD_12
IC||471|210|2|28X2 - 3V - PIC 18F25K20|U?|||DIP28|IC||DIP28_2
Wire||586|402|21||11|#000000|2|11||10|
Wire||613|402|21||11|#FF9900|3|11||10|
Wire||640|17|21||11|#000000|3|11||10|
Resistor|2200|267|366|1|Resistor|R?||3||IC||
Wire||263|402|21||11|#00A060|3|11||10|
Capacitor|100nF|589|335|3|Capacitor|C?||1|4|||cap_413
BREADBOARDSTYLE=BB12
SHOWTHETOPAREA=false

EDIT: or you can show with a TO-220 voltage reg

Code: 
Wire||74|44|21||11|#FF0000|3|11||10|
Wire||47|17|21||11|#000000|16|11||10|
Wire||74|209|21||11|#FF0000|3|11||10|
Resistor|1000|105|339|1|Resistor|R?||3||IC||
Wire||130|363|12||11|#FF9900|3|11||10|
Wire||76|180|11||11|#FF0000|4|11||10|
Capacitor|1K63: 100f|185|142|1|Capacitor|C?||2|1|||cap_121
Wire||263|17|21||11|#000000|3|11||10|
Wire||317|402|21||11|#000000|2|11||10|
Capacitor|100uf|104|383|1|Capacitor|C?||2|3|||cap_321
Note||82|252|1||||1||1 - LM317T||NOTEPAD_11
Note||108|284|1||||1||2 - LM317T||NOTEPAD_11
Note||137|311|1||||1||3 - LM317T||NOTEPAD_11
IC||471|210|2|28X2 - 3V - PIC 18F25K20|U?|||DIP28|IC||DIP28_2
Wire||586|402|21||11|#000000|2|11||10|
Wire||613|402|21||11|#FF9900|3|11||10|
Wire||640|17|21||11|#000000|3|11||10|
Resistor|2200|213|311|1|Resistor|R?||3||IC||
Wire||91|374|22||11|#00A060|4|11||10|
Capacitor|100nF|589|335|3|Capacitor|C?||1|4|||cap_413
Transistor|BC559|76|318|1|Transistor|Q?|||2|IC|In Ou Adj|transistor_21
Wire||158|374|23||11|#000000|3|11||10|
BREADBOARDSTYLE=BB12
SHOWTHETOPAREA=false
 

Attachments

Last edited:
slimplynth

slimplynth

Senior Member
No worries from me and well spotted on the green wire... think i used an orange wire but my diagram could have left someone scratching their head for a while maybe.. thanks again.

I do love the PEBBLE's. got to transfer the rest of my robot's innards on to it - before I vero everything.. feels a bit nerve-racking after spending time getting it all to work only to pull it apart -slowly.
 
B

BeanieBots

Moderator
slimplynth said:
Have tested and the circuit gives a steady 1.89V supply to the 28X2 which is close to the lower limit stated in Manual 1 - as low as 1.8V

The Regulator is an LM317T - I'm not sure what this setup is going to be used for... but it's likely the 28X2 will be configured to output to as many 4066's as I can breadboard (just bought a big 'un)
Click to expand...
You might have some tears yet:eek:
The 4066 requires a minimum of 3v.
Level shifting would be an option but not fun if you have a lot of them to do.
 
slimplynth

slimplynth

Senior Member
BB! cheers for your eagle eyes. Should have ordered some vertical pots today but forgot. Have changed the 2.2K resistor to a 10K... getting 2.98V, will update my post above.

Now I've found my 5V 28X2 was thinking of taking advantage of the 3V version being able to do 32Mhz internally.. which means use of the SERVOPOS command at full pelt.. these 9g micro servos operate much better at that speed.

Thanks again
 
W

westaust55

Moderator
@slimplynth,

While I obviously do not know what you are doing that involves a large number of 4066 IC's, there are alternative chips that may be useful.

As you are aware, the 4066 comprises:
4 separate bi-directional analogue switches, each with its own on/off control.

If you look at alternatives like the 74HC4053 (I have used this chip),
3 separate bi-directional analogue change-over switches (A-B type like a SPDT toggle) , with a common control to switch all 3 between A and B "posiitons" so it looks like a triple pole double throw switch.
These (74HC series) also work down to 2V on Vcc.

Others include the 4051 as 8 channel (de)multiplexer and the
4052 as 2 x 4-channel (de)multiplexer. ALso available in the 74HC series.

These alternatives just may save you some time switching multiple induvudual 4066 elements at the same time.
 
slimplynth

slimplynth

Senior Member
28X2 >>> Setfreq >>> Problem >>> LEDs on the blink

Thanks for the tips Westaust; I'll have a look at these but have had six 4066's breadboarded for a while now - only because they came as a ten pack and I keep buying components but never using them :) That's a side issue at the mo because I'm not restarting work on that part of the project (PC/keyboard interface) until this blasted robot does as it's Master commands.

I've noticed a problem with the 28X2-3v setup above.

When I connect an LED+resistor between B.5 and ground the setfreq m8 instruction seems to cause problems with a simple LED on/off program. At SETFREQ M4.. everything is as expected.. however, when using M8, the pause value between blinks doesn't seem to make a difference...

A pause delay = 3000 gives the same rapid blinking as a pause delay = 10000 (i'd say its blinking 3 times per second for both values)

swap it to M4 and everything is kind of normal (the example code below the pause on/off duration being 1 min 20 secs. Am confused, I don't know what I've done wrong.

(Shame I can't blame this one on an hangover Dippy ;))

Code: 
'**************************************************************
'*                                                            *
'*                   28X2 - LED Test Prog                     *
'*                                                            *
'**************************************************************

#picaxe 28x2

' Converted by X2 Conversion Wizard Version 1.0.3 (2009r5.1)

let dirsB = %11111111
let adcsetup = 0

symbol test_led = b.5
symbol delay    = 40000

init:
setfreq M4 'Changing to M8 causes headache
goto main

main:
high test_led
pause delay
low test_led
pause delay
goto main
 
hippy

hippy

Technical Support
Staff member
Using 28X2-3V firmware B.A, everything behaved as expected with M4 and M8; on/off for 40s at 8MHz, 80s at 4MHz.
 
slimplynth

slimplynth

Senior Member
Sorted now

same firmware rev, cheers Hippy - but feel like I've wasted your time now - apologies :eek:. Had to go home to get a multimeter and some pots from maplins, it was the batteries, 4 x AA NiMH had dropped to 5.1V

The four freshly charged are showing 5.6V giving 3V with the LM317T regulator. (2V with the old batteries - too close to the minimum). It hadn't occurred to me at the time, that it would be the batteries because the original problem arose when trying to cure servo jitter, the servos seemed quite lively on the unregulated supply from the old batteries. Not knowing if it was the servo's generating too much noise, put the LED in to monitor program processing... removed servos.. realised it was M8/M4... though now obvious the picaxe was thirsty... and breath :)
 
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