Only have 2.7 volts on pin out...

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Scuzzy47

New Member
I recently broke my picaxe 40x, I ordered a new one, and I'm testing my board, I connected my LCD and stuff, but my relais or contactor (don't know who it's said in english) doesn't work, because it requires 5 volts and the board only gives 2.7 volts on each pin out that is high..
What could be the problem? I tried other batteries and such, no luck...
 
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ylp88

Senior Member
Use a DMM to measure the voltage at the PICAXE's power pins. What does it read?

<b><i>ylp88 </b> </i>
 
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bgrabowski

Senior Member
Assuming you mean &quot;relay&quot;, you should use a resistor, darlington transistor and diode as shown in the manual to energise the coil. This only needs about 1.4V.
 
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Bloody-orc

Senior Member
if you connected the relay directly to the picaxe then you can say goodbye to this pin (or port, or picaxe) as this aint gonna work nomore.
 
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Scuzzy47

New Member
But the relay works on 5V, so I don't see why it shouldn't work (except for the 5V needed, only having 2.7V)
I already connected it straight to the pin a few times, but it didn't work. My lcd works, and leds will do fine on 2.7 volts, I'll look at the circuit for a relay, thanks.
Please excuse me for my ignorance...I'm new ;)
 
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SD2100

New Member
If you put the relay directly on a battery it will probably work but a picaxe output can only source about 20mA, this will drive an LED ok but not a relay, See &quot;Picaxe manual3 -interfacing circuits&quot; it shows how to connect a relay to a picaxe output via a transistor. Don't connect a relay directly to a picaxe output.

Edited by - Phil75 on 30/04/2006 18:49:25
 
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Rickharris

Senior Member
Ok in the spirit of this forum lets go to improve the &quot;new&quot; bit :)

electricity has 3 essential parameters - voltage - The pressure you drive the electrons round with- Units of measurement = volts, current - the rate at which the electrons flow- units of measurement = Amps and resistance the resistance to that flow - units of measurement = Ohms.

These are all related such that if you increase resistance you reduce the flow (current), If you increase the pressure (voltage) you increase the flow rate (current).

Ohms law related these three things together.

The relay will need a certain amount of current (flow) for it to work. This is a functions of its resistance and the voltage supplied. (ohms Law).

As the Picaxe can only supply up to 20 milliamps of current (thats 20/1000's of an amp. although this will turn on an LED it isn't enough for your relay. the relay will try to draw as much current as it needs and MAY kill the picaxe output - It burns out the transistor switch that drives the output in the IC.

This is why you may well put a resistor in series with an output to limit the ammount of current that can flow such as when you use an LED.

Because the Voltage/Current and resistance are related you can run an LED on different voltages if you put a suitable resistor in the circuit to reduce the current flow to a safe level.

The current that flows through a series resistor also flows through the LED - a difficult concept to get your head around at first.

Edited by - rickharris on 30/04/2006 19:51:42
 
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Scuzzy47

New Member
Thanx a lot for the explanation, I'm beginning to understand more. But what I do not understand, is the circuit. It's a circuit for when your relay uses 12V, mine only needs 5V. So I don't have a clue what to change for it to work with 5 volts...
Could someone help me with this? My project works, except for the relay...
 
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Bloody-orc

Senior Member
use the same schematic but just connect your relay instead of this 12V one. and also where it states that 12V must be connected there you just connect 5V instead. and there you go. a 5V relay driving circuit that wont burn your picaxe ;).
 
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Rickharris

Senior Member
The transistor is acting as a switch, It provided the path for the extra current the relay needs - the voltage isn't an issue in this case.

The picaxe can switch on the transistor because the transistor only needs a small current to turn it on.
 
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Scuzzy47

New Member
Got it :). Now all I need is the transistor, I don't think I can get the bcx38b in Belgium, so I suppose I will use the 2 transistors; BC639 (http://www.ortodoxism.ro/datasheets/siemens/BC639.pdf) , BC548B
(http://www.ortodoxism.ro/datasheets2/d/0kq9ua20u27ka13c66efh960khpy.pdf).
Is it ok if I use a BC547B or a BC458A? Cause the shop I will be buying them only has the following transistors in the BC series: (http://ic.dos.nl/catalog/page/info_ic_artikelen.php?PHPSESSID=9f1c16d4828bb28defd7df6c54012db1&amp;id=44774&amp;selected_id=44832#table_entry_44832)
And could I use the 1N4004 instead of the 1N4001, since they don't have that one either... The current is 400V instead of 50V but it's current is also limited to 1A, so that should work, wouldn't it? Here's a datasheet for both ( http://www.ortodoxism.ro/datasheets/vishay/1n4001.pdf)
Thank you guys for all your help, this forum is great!
 
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manuka

Senior Member
A quick message scan fails to show if mentioned - you'll have to tell us the current demands of the relay or measure the coil resistance. BC547s etc can handle ~200mA &amp; are easily controlled by a Picaxe output to their Base if the relay is under this.
 
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Scuzzy47

New Member
I'm sorry, forgot to give the link for the datasheet, here it is(http://www.velleman.be/be/en/product/view/?id=17774).
I also measured the resistance, it's 80,4R and it needs 6VDC (as it says in the datasheet).
Thx for the quick reply..
 
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tomohawk

Senior Member
So if i use a relay with 5v coil voltage and transistor it will be able to drive a 12V solenoid valve? even though the output isnt 5V??

 
 
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Dippy

Moderator
Assuming you've read and are happy with page 7 of the Interfacing Circuits manual, you use the relay pins to act like a simple switch to provide power to your 12V solenoid valve.

The relay is an electrically operated switch. If you are able to sketch a circuit with a simple switch to operate your solenoid then just substitute the relay pins for the switch.

Check the relay markings and data sheet to ensure you use the right pins.
The drawing on page 7 shows a N/O Normally Open relay connection. That's like a switch in the OFF position.

And DON'T mix up the 5V to the PICAXE with the 12V to the N/O pins of your relay. Or else Bye-Bye PICAXE!!

If I may suggest doing this in stages. Do the circuit on Page 7 and see if you can programme your PICAXE to make the relay click on and off. Leave the 12V part until you've got this bit working. Double check everything before applying power.


Transisitors: Get a data sheet on the BCX38 to look at the ratings. There are probably dozens of low/medium power NPNs that will be fine. No doubt everyone will list their 'favourite NPNs'.

Obviously you are very new to all this, so it would be IDEAL if you had a bench power supply where you can set a low current limit for prototyping. It could prevent embarrasing and costly accidents. I know they cost a few quid but so do 10 smoking PICAXEs.

Good luck... and be patient.
 
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manuka

Senior Member
&quot;Scuzzy&quot; : I assume your 80,4 means 80.4 Ohms? The coil current hence should be I = V/R = 6/80.4 = ~75mA which a bog standard BC547 style NPN will handle OK.

See a suitable setup (used then for a small DC solar motor)=&gt; www.picaxe.orcon.net.nz/motorpwm.jpg <A href='http://www.picaxe.orcon.net.nz/motorpwm.jpg ' Target=_Blank>External Web Link</a>.

Although he used a higher gain Darlington, Rev.Ed's Clive wrote of this as part of his late 2005 Silicon Chip schools series =&gt; <A href='http://images.google.co.nz/imgres?imgurl=http://us1.webpublications.com.au/static/images/articles/i1051/105158_6lo.jpg&amp;imgrefurl=http://www.siliconchip.com.au/cms/A_105158/article.html&amp;h=287&amp;w=302&amp;sz=24&amp;tbnid=wauL5cZNOTO2MM:&amp;tbnh=106&amp;tbnw=112&amp;hl=en&amp;start=7&amp;prev=/images%3Fq%3Dpicaxe%2Bmotor%26svnum%3D10%26hl%3Den%26lr%3D%26rls%3DGGLD,GGLD:2004-52,GGLD:en%26sa%3DN ' Target=_Blank>External Web Link</a>

You can make your own Darlington with 2 x NPNs of course =&gt; www.nexusresearchgroup.com/images/picout1.gif <A href='http://www.nexusresearchgroup.com/images/picout1.gif ' Target=_Blank>External Web Link</a>. This schematic also shows the typical Picaxe output linking.



Edited by - stan. swan on 01/05/2006 22:56:12
 
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Scuzzy47

New Member
I was thinking ons doing it like in the last picture, tomorrow I'll ask my teacher what components to use exactly, since I'm not able in getting the BC548B nor the 1N4001, I'll ask him so I don't mess things up...
Thanks all, Scuzzy
 
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manuka

Senior Member
<BLOCKQUOTE><font size=1 face=arial>quote:<hr height=1 noshade>since I'm not able in getting the BC548B nor the 1N4001 <hr height=1 noshade></BLOCKQUOTE></font><font face='Verdana, Arial, Helvetica' size=2> ! These are perhaps THE most common semiconductors on the planet. Surely they're in stock ? Where ARE you located ? Almost anything equivalent will do of course. Stan

Extra: Try a single NPN first =&gt; www.picaxe.orcon.net.nz/npnamp.gif <A href='http://www.picaxe.orcon.net.nz/npnamp.gif ' Target=_Blank>External Web Link</a>


Edited by - stan. swan on 02/05/2006 12:07:07
 
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Mycroft2152

Senior Member
The BC series of transistors are not very common in the US. The general purpose transistors used are 2N2222, 2N3904, 2N2907, anf the 2N3906.

Myc

Edited by - mycroft2152 on 02/05/2006 12:10:23
 
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