Wake 08M with Remote Control?

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peterclones

New Member
I just joined this forum and am in the process of ordering my first 08M project board. I'm new to all this and want to use a remote to control the Picaxe. I'm wondering if it will be possible to turn on the Picaxe with the remote control's power button? I'd like to have it in sleep/lower power mode normally, then turn on with a press of a button.

Thanks very much.
Pete
 
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AllyCat

Senior Member
Hi Pete,

Welcome to the forum. Yes, in principle it's possible, but depends on exactly how low a power consumption you require and whether it's an "off the shelf" remote control or a "custom" design.

The two basic methods are to sleep/nap the PICaxe for short periods (testing for IR each time it wakes up) and/or running the PICaxe at a slow clock speed (e.g. setfreq 32kHz) until some IR is detected. A third method of using an interrupt is not normally appropriate/possible with a PICaxe, particularly the non-X2s.

You need to measure/decide how long a burst of IR is available to "wake" the PICaxe and then it's possible to decide on the nap and/or clock speed parameters, and the general structure of the code. Note that some commercial Remote Controls automatically repeat their "message" several times (however long the button is pressed), others may continue repeating until the button is released.

Cheers, Alan.

PS: I've just noticed that you quote 08M rather than 08M2. Are you referring to the project board or to the actual PICaxe chip that you plan to use? I believe the 08M chip may have more restricted frequency capabilities.
 
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peterclones

New Member
Thank you for the reply Alan. I'm planning to buy the PICAXE-08M Servo Driver Kit from Robotshop.com. It doesn't specify which chip exactly, although the link to the chip points to 08M2. I hope that's what it comes with.

My plan is to have 3 mini or micro servos running a kind of mini robot arm, along with the IR Receiver. I don't want to manually turn it on and off each time, but I don't want too much power going to the chip or servos when not in use either. Which brings me to another the question: How do I ensure no current is drawn by the servos when not in use? Do I simply put them in the neutral position? I've read that servos are unpredictable in this way.

Thanks.
Peter
 
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BeanieBots

Moderator
Welcome to the forum.

You can dissable the drive to servos by simply turning off the position demand pulses.
This might happen when you put the PICAXE to sleep but will depend on which method you opt for.
Alternatively, simply issue a "servo off" command. (see 'servo' in the manual for more details).
When servos are inactive they still draw a mA or so. If you want very low power, consider using relays (or a transistor) to remove their power.
Setting the servo to 'neutral' will simply make it drive to the neutral position. There is nothing "unpredictable" about servos being driven to neutral. (or have you been reading about modified constant rotation servos?).
 
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srnet

Senior Member
How do I ensure no current is drawn by the servos when not in use?
Click to expand...
You need to set the servo control pin to 0v and disconnect the power.

Do I simply put them in the neutral position? I've read that servos are unpredictable in this way.
Click to expand...
Servo 'Neutral' has no absolute electrical significance to the servo, its just the mid physical position between the two physical limits of rotation. In a sense the 'neutral' position is unpredictable, in that that a 1.5ms servo pulse may not put the servo exactly in the physical mid position.
 
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peterclones

New Member
Ok, thanks guys. I think I'll just send the servo off command. I don't mind a mA drawing, just want low power mode on everything.

Much appreciated.
Pete
 
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peterclones

New Member
Another quick question about servos. How can you determine the max current a servo will draw? I'm using HS-85BB servos and the specs say .8mA IDLE and 240mA No Load Running. Woud you, say, double it for a load, just to be safe? Not sure about that one.
 
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srnet

Senior Member
peterclones said:
I don't mind a mA drawing, just want low power mode on everything.
Click to expand...
Servos vary mind (regardless of what the data sheets say), for most servos the inactive current could be anywhere between 1mA and 10mA in my experience.

How can you determine the max current a servo will draw?
Click to expand...
You need to measure it under the typical load.

Put one on the bench, connect it to a PICAXE set it to mid position and pull on the servo arm with the typical load and measure the current. I would then at least double it to allow a margin for peak loads. Then multiply by 3 to allow for all 3 servos running at once.
 
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peterclones

New Member
Great, thanks. One last question. Can someone recommend an IR receiver from Robotshop.com that will work with the Picaxe, with or without remote? Their support tech tells me this one will:
http://www.robotshop.com/productinfo.aspx?pc=RB-Dfr-92&lang=en-US

I suspect that remote isn't Sony compatible. Just a hunch because that tech guy didn't seem to familiar with Picaxe.

Or perhaps one of these? I like the remote sizes here:

http://www.robotshop.com/productinfo.aspx?pc=RB-Ghi-65&lang=en-US
http://www.ebay.com/itm/REVOLUTION-AXE040-Picaxe-Infrared-Remote-Control-Upgrade-Accessory-Kit-130840-/130786587940?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item1e737cf524#ht_2377wt_1023
 
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