Cheap USB Picaxe adapter

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gengis

New Member
My USB to RS232 adapter died recently, and I had a couple of cheap single board adapters around that I intended to build into projects, to make Picaxe reprogramming with a USB cable easy.

Cost of the adapter, called a USB to RS232 TTL 232 Converter Module PL2303 Chip PC was $5.69 USD each, with free shipping from China, at Markmart.com

It includes jumper wires to connect to a header, on board 5 and 3.3 volt power and LEDs to indicate power, receive, and transmit.

The adapters used the same Prolific PL 2303 chipset I've been using all along - so no need for a new driver and it is compatible with my ordinary USB to RS232 adapter.

BUT they invert the signal... Using the com port "test" in the programming editor the input to the axe is "low" when the on screen light is "on" and visa versa (or backwards). The "terminal" however, worked fine when I shorted the transmit and receive pins on the module, so I knew it was working or would work if the polarity was reversed.

I wired a couple of 2N3904 inverters to invert the signals and it works like a champ.
 

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Andrew Cowan

Senior Member
I did exactly the same to mine recently, when I didn't have my axe027.

I had to use the PICAXE's 5v supply rather than the module's - for some reason the voltage of the module's 5v supply fell to a few volts when I tries to draw a few mA through the transistors.

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hippy

hippy

Ex-Staff (retired)
wall_axe said:
I'm always in search of a cheaper/better USB adapter.
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It's often easier to find cheaper, but not always better, and sometimes not as good.

Apart from the chipset needing to be compatible, have correct polarity, plus the issues of driver software, the electrical characteristics are often not known. Some cables may not be 5V tolerant and equally may not work or not work reliably down to the low voltages a PICAXE can.

While alternatives to the AXE027 can and do work, are suitable for specific situations, they may not be suitable in all. As previously discussed, one may simply be offsetting cost savings against later difficulties, costs, loss of time, project disruption and frustration when a cable doesn't work. Great when it does work, but not so good when it doesn't.

The AXE027 remains our ( and my ) recommendation; tried and tested and hasn't let me down yet where other USB cables have.
 
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gengis

New Member
Biting the hand that feeds me

The AXE027 remains our ( and my ) recommendation; tried and tested and hasn't let me down yet where other USB cables have.
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When I got my first axe the AXE027 wasn't being imported here - along with a lot of the other axe related goodies. But good quality Prolific adapters are in the $9 price range and that's what I had. Now, I can't see paying >$20 for what the $8.99 thingee does very well.

But the "El Cheapo" made in Hong Kong USB/TTL adapter was intended to be incorporated into a project and left there as a quick and dirty way to make it USB compatible - not something I'd spend $20 for in that application.

How special is the AXE027? Where are they made, etc.? What sets them apart?

Looks to me like there's only one chip, one crystal, and a handful of passive parts, leds and some diode clamps. Now if you are comparing an AXE027 to one of the $2 adapters that has a blob of epoxy hiding the board mounted silicon die, I'd be more inclined to agree.
 
hippy

hippy

Ex-Staff (retired)
I agree, $9 looks far better than $20, and I'm after bargains as much as the next man !

How special is the AXE027 ? That's hard to quantify. It comes with full technical support and help getting it working, replacement if you ever get one which is faulty, tried and tested as I say, and even has the 3.5mm jack fitted. That's an extra cost with other cables and the absolute costs - even relative costs of 'paying extra for the privilege of having an actual AXE027' - aren't that great in the scheme of things. AIUI the AXE027 isn't marked-up to maximise profit and we probably only sell one per customer at most. It's ultimately not in our interests to inflate PICAXE entry costs to make short term profits.

It's fair to acknowledge that any profit we do make, AXE027 or otherwise, pays for everything we do, and obviously the more of that the better and we'll prefer to have that profit than see it go to someone else. We don't however heavy-handedly play the 'guilt trip' card, nor simply refuse help when others decide to go a different path.

I've got a number of USB010 and similar PL2303 cables and have had some problems at lower PICAXE voltages. I haven't had any driver or similar issues but some people report they have. That's not to say they are bad or don't work. most are very well built, and if they work for a particular project that's all well and good as previously acknowledged - and the same goes for whatever's necessary when you need to do that.
 
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wall_axe

Member
I'm all for companies making a profit. Its critical for survival and development of new products. That being said, I've always been a "roll your own" type of guy. While a premanufactured cable is definitely more convenient than my approach, I would argue that you can learn more by doing it on your own. The first time I tried this adapter it didn't work. I realized it wasn't inverting the signal. I dug around and created a circuit to invert it. Never did that before; now I know.

As an added advantage a generic adapter can be used with other devices. I've been playing around with Picaxe, Stamp, Arduino and (soon) propeller. A little more versatile than always getting a specific adapter for a specific chip.

Just my $0.02.
 
hippy

hippy

Ex-Staff (retired)
Thumbs-up for "roll your own", and I've done that too - a personal 'background project' to find a Nokia USB data cable to hack and actually make work was one task I embarked upon which turned out to be a long haul and more effort than I imagined !

Let's be clear that we aren't saying "don't"; just recommending our opinion of the smoothest path to follow.

I'd also add that it's much smoother sailing when you've got an AXE027 plus the cable you are hacking as you're not totally dependent on making that cable work, and, if it doesn't, you have something to do a comparison test against, can check whether it's a PICAXE or PC problem or the cable itself.
 
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John O

Senior Member
My only criticism of the AXE027 is the cable looks like it's strong enough to tow the QE2. It's a bit disconcerting when the project board it's connected to started getting dragged across the bench and rearing up like a cobra ready to strike :)

I know older-style USB cables used to be like lengths of rope but modern ones supplied with phones, cameras, GPS etc are a lot thinner. How about a nice flexible AXE027 ? :)

John.
 
hippy

hippy

Ex-Staff (retired)
On the plus side the AXE027 cable and plug are both seemingly immune to being run over by the castors of a sat-upon office chair and when it is ripped out it loosens / breaks the jack socket silver end cover rather than breaks the cable.

( again, tried and tested, but don't tell Technical :) )

It's likely a case of swings and roundabouts; robustness or lightweight. It can be a little heavy and inflexible at times but that can be overcome by making sure it runs from the back of the desk / work bench rather than hanging over the front.

One solution may be a lightweight stereo socket to plug extension cable. Something for headphones would probably work.
 
H

Haku

Senior Member
Something confuses me a little about the cheap USB adaptors linked to, are they putting out full RS232 serial voltage levels or TTL voltage levels?

Have to agree with John on the AXE027, you could tie a couple together and tow a car with them! :) one side effect/advantage of this is that you start paying attention to the robustness of any project you're working on, a stereo programming socket not held down strong enough could get damaged by that AXE027 lead if snagged at any point.
 
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Andrew Cowan

Senior Member
I'd like to request an even tougher, armour plated version of the axe027 - my (previous) axe027 was pulled into one of my robot's sprockets during testing - the steel sprocket, 1/2" chain and 750W motor chewed through the cable very easily.

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wall_axe

Member
Haku said:
Something confuses me a little about the cheap USB adaptors linked to, are they putting out full RS232 serial voltage levels or TTL voltage levels?
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Typically TTL voltage levels. You'll need a MAX232 or similar to get the full serial voltages.
 
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inglewoodpete

Senior Member
wall_axe said:
Typically TTL voltage levels. You'll need a MAX232 or similar to get the full serial voltages.
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That's not my experience. The AXE027 is the only cable that I've found that gives TTL levels (0-5v).

The others that I've used give RS232 levels (-12v / +12v) or pseudo RS232 (-5v to +5v) or similar.

Note that adding a MAX232 will invert the polarities.
 
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hippy

hippy

Ex-Staff (retired)
This highlights the problem of 'unbranded USB cables'; you don't know what they will be putting out. In my experience PL2303 cables, similar to USB010, put out +/-10V, the rest I've found to be 0V/+5V or 0V/+3V3 with idle high polarity. Only the AXE027 I have is idle low polarity. Other than the PL2303 cables I've not encounterd any which put out a negative voltage.

The Nokia cables I have are particularly odd, needing in-line series resistors or they simply don't work in TX-to-RX loopback tests, put an exclamation mark up in Device Manager if plugged in while looped-back.

The only way to tell what a particular USB-to-Serial cable puts out is to read the datasheet or to test it when you get it.
 
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