Running an 08M from a 6v supply?

[Fletch]

I need to build a small 08M circuit to drive a couple of small 5v relays. the power supply I have available is 6v which is probably too small a difference for even a LDO regulator.

1) Can the 08 work from 6v at a push?

2) Could I use something like a resister or the voltage drop across a diode to knock the voltage down 1v?

 

[Rickharris]

Use a regulator 5v max only a single 3 pin ic easy to use. http://www.rapidonline.com/productinfo.aspx?kw=voltage%20regulator&tier1=Electronic+Components&tier2=Integrated+Circuits&tier3=Voltage+Regulators%2c+Fixed&tier4=100mA+Fixed+voltage+regulators&moduleno=74620

5p so won't break the bank.

6v may work for a while BUT will more likely make the 08M hot and unreliable - and dead.

 

[Peter M]

I need to build a small 08M circuit to drive a couple of small 5v relays. the power supply I have available is 6v which is probably too small a difference for even a LDO regulator.

1) Can the 08 work from 6v at a push?

2) Could I use something like a resister or the voltage drop across a diode to knock the voltage down 1v?

1 or 2 diodes in series with the supply will knock around 0.6v-1.2v off, brining it within the 5.5v max (operating voltage) specified by microchip (the chip manufacturer of the blank 08M chips)

Note. the absolute max voltage for this chip is rated at 6.5v, but this is not its operating voltage!!

 

[MartinM57]

Use a regulator 5v max only a single 3 pin ic easy to use. http://www.rapidonline.com/productinfo.aspx?kw=voltage%20regulator&tier1=Electronic+Components&tier2=Integrated+Circuits&tier3=Voltage+Regulators%2c+Fixed&tier4=100mA+Fixed+voltage+regulators&moduleno=74620

5p so won't break the bank.

6v may work for a while BUT will more likely make the 08M hot and unreliable - and dead.

Vdo for that device is 1.7v, so it's not going to work well in producing 5v from 6v.

But they're very cheap - if this post had been yesterday, I'd have bought a selection in the big order I did to Rapid yesterday afternoon

 

[Technical]

Do not ue an 08M at 6V. It will get hot and not operate correctly.
A 4.5V battery box is just as cheap as a 6V battery box, or use a diode as suggested.

 

[Fletch]

The circuit is being fed from the servo output of a RC receiver, so the voltage I have it what I have, I don't have room to fit a second supply.

I thought the diode idea would work, just wanted to make sure.

 

[ljg]

I second Preter M's two diode solution as the easiest way.

 

[nfk]

On this subject of voltage regulation, although many radio control servos operate on 6 volts I am aware that in the future this may go even higher because manufacturers want to align themselves to Lithium Polymer technology rather than NiCad or NiMH.

To 'future proof' a circuit I am building for the 28X1 I assumed I could use a 5-volt regulator to power a 28X1 (the one I have in mind can cope with up to 12 volts input and has only a .23 volt drop-out which seems great to me).

A simplified version of the circuit I have in mind is here with the receiver connected to the three-pin connector on the left and the servo to the one on the right:

(Full size image here)

I have three questions:

1. Would it be a bad idea to use a voltage regulator for any reason?

2. Although in this setup the chip is powered from a 5-volt supply the signal coming from the receiver is likely to be 6 or more volts on the high part of the pulse. Is this undesirable?

3. Just a very minor point, why does the 28X1 have two earth pins (8 and 19)? As a matter of interest is this significant and what would happen if one of them wasn't connected?

Cheers,
Nigel

 

[MartinM57]

What part number is the regulator (with a Vdo of 0.23v) - or is it a secret

 

[Technical]

1) Not if it actually does work at 0.23V reliably!
2) Yes, it is undesirable. However a resistor in between the PICAXE input pin and the servo signal will help resolve this.
3) Ask Microchip, probably because there was spare pin they didn't know what to do with! However the Microchip datasheets do state both should always be connected.

 

[MartinM57]

3. It's easier to design the grounded parts of the die by having connections exiting the die on two different sides ie - hence two GND pins on the package?

and/or

3. (was going to say that more current flows out of the GND pins than the internal link from die to package pin can handle, so they use two - but having typed it in, I'm not convinced )

 

[hippy]

I'm inclined to believe the 'spread current' theory for separate 0V's and +V pins, especially when there are ( on some chips ) multiple ports each capable of handling 100mA each.

Split dies are sometimes used AIUI and they must have all power pins connected to work as intended, but often multi-power pins work with only one connected.

 

[Technical]

Put your multimeter across the two ground pins... ;-)
You'll hear a beep on the continuity test!

(obviously the chip needs to be by itself, not in a circuit and not powered)

 

[BCJKiwi]

Hmm... What multimeter do you have?

Many use a 9V Battery and deliver 9V at certain ranges!! = Caution advised

 

[Michael 2727]

I'd be inclined to go with the current spreading idea also.

I have a windowed UV erasable PIC12C508 chip (not common)
If you look at the fine gold wires connecting the Silicon to the
Legs of the chip they are very thin, I would be interested as
a matter of curiosity to know what current these wires can
actually carry. I would suggest as Hippy says that the total
chip power dissipation could easily vapourize a single wire on
some chips so two or several may be needed in some instances.

It would also be interesting to see how much heat is actually
developed in the connecting wires rather than the silicon itself.

 

[hippy]

I think Michael's "in some instances" sums it up well.

Like do I need reservoir caps for a regulator, do I need decoupling caps on the power rails, do I need to look when crossing the road ... often not, but it does no harm and there may be cases where it is important, other times it works well without, but situations are rarely well defined.

It's always better to follow the recommendations. Don't and get away with it then well done. Don't and it all goes badly wrong then on your own head be it.

 

[D n T]

NFK, try it and find out

Stan will love this...
If you have some breadboard, try the 28 with only one earth, if it downloads a flasher program, try it on one pin with the flasher wired up, then add another and another... until all the outputs are being used, then try a debug for each analog input etc.
Please, when you find out, could you let us know

 

[tikeda]

It may be out of the acceptable price range but has anyone played with the switching regulators from Dimension Engineering? Their units run <$20US.

I've thought about using their 'Negatron' for some projects.

 

[Andres Rodriguez]

Carefull with the 6V from the receiver, 6V on a 5 cell pack is the nominal value. A freshly chrged 5 cell pack will exceed 6V. We have used 5cell packs (NiCad and NiMH) to get more torque from the servos but the on-board systems (Rx and servos) work fine with 4.8V. If you don't need max torque stay with a 4 cell pack. Or you could power the RX and the Picaxe with a 2 cell LiPo and an LM7805 regulator.
Is the vehicle powered with electric motor or internal combustion?

 

[Fletch]

Carefull with the 6V from the receiver, 6V on a 5 cell pack is the nominal value. A freshly chrged 5 cell pack will exceed 6V. We have used 5cell packs (NiCad and NiMH) to get more torque from the servos but the on-board systems (Rx and servos) work fine with 4.8V. If you don't need max torque stay with a 4 cell pack. Or you could power the RX and the Picaxe with a 2 cell LiPo and an LM7805 regulator.
Is the vehicle powered with electric motor or internal combustion?

It's a kite, well a photographic rig slung under a kite. I bought a 2 cell LiPo pack because I'm counting every gram and that happens to be the smallest/lightest pack with a reasonable flight time.

Now the only regulator pack they had drops the voltage to 6v, so it will be a regulated output, that's ok for receiver and servos but a bit high for the logic. Now the prebuilt regulator is tiny. I doubt I can make anything quite as light as that with stripboard. If it was possible to keep it while keeping the Picaxe circuit as small and light as possible, that would be the optimal solution. The fallback is to build the regulator circuit onto the Picaxe board and then have that power the receiver and servos but that would probably be heavier.

I'm assuming that a 6v input - 0.7v by passing it through a diode will deal with the power requirements of the picaxe circuit, what kind of resistor would be good for the signal input?

(the picaxe circuit will take a servo pulse stream and use it to operate 2 small relays, one attached to the "focus" line of a digital camera the other to "shutter." On receiving a pulse for say "go right" the picaxe would activate the focus relay followed a second later by the shutter.)

 

[Peter M]

Hi Fletch, sounds like an interesting project...
If you use a diode such as a 1N4004 or simular it will drop around 0.6 - 0.7v and can handle up to 1 amp which is far more than the picaxe will ever need..
Also if you are switching relays from the pic make sure you use a diode across the relay coil/s (arrow or banded end toward +ve) so that the back EMF does not destroy the chip.

The relay coils need to be greater than 250 ohms as well to keep the current at or below 20mA per pin or use a transistor / fet to switch the relays from the pic


NFK, another reason for using more than 1 earth pin on chips (particularly when the pins are in the centre of the chip) is for heat sinking as earth is often attached to the die, therefore if only one is used it can compromise the specs of the chip. But now that I have measured one it would seem that its a split die as Hippy said.

 

[Fletch]

I'm planning to use 2 of the silicon relays suggested by someone in another article. This should mean no need for a transistor to activate a coil or a back emf diode. Like I said, trying to keep it small.

I'm assuming that a 330ohm resistor on the signal from the RC receiver should be enough?

 

[Andres Rodriguez]

I'm assuming that a 6v input - 0.7v by passing it through a diode will deal with the power requirements of the picaxe circuit, what kind of resistor would be good for the signal input?

(the picaxe circuit will take a servo pulse stream and use it to operate 2 small relays, one attached to the "focus" line of a digital camera the other to "shutter." On receiving a pulse for say "go right" the picaxe would activate the focus relay followed a second later by the shutter.)

You can use the diode between the battery and the receiver then connect all three wires from the receiver to the Picaxe. I am powering a picaxe 28X1 by connecting the the signal wire directly to the input pin, and the V+ and Gnd from the same channel powers the Pic

 

[Fletch]

Clever, also gives me reverse polarity protection for the receiver.

 

[Wrenow]

It's a kite, well a photographic rig slung under a kite. I bought a 2 cell LiPo pack because I'm counting every gram and that happens to be the smallest/lightest pack with a reasonable flight time.

Now the only regulator pack they had drops the voltage to 6v, so it will be a regulated output, that's ok for receiver and servos but a bit high for the logic. Now the prebuilt regulator is tiny. I doubt I can make anything quite as light as that with stripboard. If it was possible to keep it while keeping the Picaxe circuit as small and light as possible, that would be the optimal solution. The fallback is to build the regulator circuit onto the Picaxe board and then have that power the receiver and servos but that would probably be heavier.

I'm assuming that a 6v input - 0.7v by passing it through a diode will deal with the power requirements of the picaxe circuit, what kind of resistor would be good for the signal input?

(the picaxe circuit will take a servo pulse stream and use it to operate 2 small relays, one attached to the "focus" line of a digital camera the other to "shutter." On receiving a pulse for say "go right" the picaxe would activate the focus relay followed a second later by the shutter.)

Can you not just swap the included 6v regulator with a 5v regulator?

Cheers,

Wreno

 

[Fletch]

Can you not just swap the included 6v regulator with a 5v regulator?

Cheers,

Wreno

It's a small encapsulated surface mount board about the size of a postage stamp. I don't know I could solder that small, I did see a couple of 5v ones but they are all quite a bit bigger.