HP 50G - Any way to increase the IR TX/RX range?

[Sukiari]

Apologies if this has been covered before. I looked on the forum here and used a Google search as well, and came up dry. I confirmed by my own tests that the HP-50G's IR range is extremely poor compared to the HP-48 series but I wonder why? Is the IR diode in the 50 weaker than the one in the 48? Does the IR window on the top of the calc perhaps attenuate all the IR? What's the secret behind this issue, so we can fix it?

Offhand, is there a handy way to make the printer advance a line right from the calculator? Could any 82240A/B experts chime in? If I could write a program to do this I would be very happy.

Many thanks, it's nice to participate in a forum with such a level of mathematical, technical, and calculator knowledge.

[rprosperi]

(09-17-2015 12:02 AM)Sukiari Wrote:  Apologies if this has been covered before. I looked on the forum here and used a Google search as well, and came up dry. I confirmed by my own tests that the HP-50G's IR range is extremely poor compared to the HP-48 series but I wonder why? Is the IR diode in the 50 weaker than the one in the 48? Does the IR window on the top of the calc perhaps attenuate all the IR? What's the secret behind this issue, so we can fix it?

Offhand, is there a handy way to make the printer advance a line right from the calculator? Could any 82240A/B experts chime in? If I could write a program to do this I would be very happy.

Many thanks, it's nice to participate in a forum with such a level of mathematical, technical, and calculator knowledge.

The 48 series machines use an older IR technology which goes by many names, most commonly Red-Eye. It was designed for more casual consumer use, so the range and angle are more flexible.

The 50g uses IRDA, a later standard which generally supported higher transfer rates (though not much higher on these machines), better auto-negotiation of data-rates, etc. but in many products they reduced useful range in order to meet these other parameters. It's unlikely you can do anything to change this enough to make a difference.

For advancing the printer, I would imagine sending an object containing carriage-returns should do that, but have not tested so.

[Martin Hepperle]

(09-17-2015 01:01 AM)rprosperi Wrote:  The 48 series machines use an older IR technology which goes by many names, most commonly Red-Eye. It was designed for more casual consumer use, so the range and angle are more flexible.

The 50g uses IRDA, a later standard which generally supported higher transfer rates (though not much higher on these machines), better auto-negotiation of data-rates, etc. but in many products they reduced useful range in order to meet these other parameters. It's unlikely you can do anything to change this enough to make a difference.

The HP50g is an extremely versatile machine when it comes to I/O. For printing you can use RedEye for the 82240 but also IrDA for other devices. In both cases range is rather limited, though. The cleanest way to improve the range without modifying the calculator would be a transceiver box which would boost IR signals, but such a device does not exist, as far as I know. A pass-through transceiver should be fairly easy to design for someone with some background in electronics (who wants to start another small project?).

For the various ways of I/O on the 48/49/50 series machines see the attached scheme.

Martin

[rprosperi]

(09-18-2015 11:30 AM)Martin Hepperle Wrote:  For the various ways of I/O on the 48/49/50 series machines see the attached scheme.

An excellent and useful chart Martin, thank you for sharing it!

The various devices mentioned do not include the original HP-49 - does this machine act like a 48G or the later machines? I have one, but honestly use only very rarely; I much prefer a 48G or 50g. I was away from the hobby when the 49 was released, so never learned it's details very well.

[Martin Hepperle]

(09-18-2015 01:23 PM)rprosperi Wrote:  ...
The various devices mentioned do not include the original HP-49 - does this machine act like a 48G or the later machines? I have one, but honestly use only very rarely; I much prefer a 48G or 50g. I was away from the hobby when the 49 was released, so never learned it's details very well.

Well, the HP-49 has some difficulties with IR ... it does not have IR Leds! There is a serial interface only.

There was a hobby project to attach an IR-transceiver to the HP-49's serial port. See the description (Infrared Adapter 1.2 - "Information about an adapter to convert the serial port into an infrared port" by Marcel Flipse) on some other HP38/48/49/... web site.
However this nice idea never materialized into a commercially available product.

Martin

PS: on the chart I mention flag -127 as I read somewhere (where?) that it also affects printing on some calculators. If someone knows more about flag -127 I could update or remove it from the sheet.

[Dave Shaffer]

As Martin Hepperle commented, it should be practically trivial to build a pass-through transceiver. I have some IR-sensitive phototransistors that should work as a detector, which would operate a transistor switch that turns on/off an IR emitting LED of almost whatever power level you want. A quick check on Ebay shows 3 watt and 10 watt (!) IR LEDs. The switch on/off times of these are at the few microsecond level. Parts cost would be a buck or two, not counting battery and packaging.

Does anybody know what the wavelength of the HP50 led is? And what is the signalling rate? If it is 100 kilobits per second or more, fast detectors and emitters will be needed!

I don't have a '50 or any other HP LED-equipped calculator, but I will try to play with one of my TV or CD player remotes to see if I can make a simple transceiver. I don't have any of those high-power LEDs either, but I should be able to make a red LED blink to show that I am receiving signals.

[matthiaspaul]

The attached documents contain details on the implementation of the IR hardware in the HP 48 and the HP 82240B printer.

Hope it helps,

Matthias

[striegel]

Quite a number of years ago there was an application for the HP 95LX palmtop PC that let the user control TV sets with infrared remotes (Was it IR95? ... or maybe Remote Commander?). It recorded the IR signals from a TV's own remote and could play them back by pressing the assigned keys. Sets of these recorded sequences could be saved to files and kept for handling different devices.

When the 100LX (and also the later 200LX) was introduced, its effective IR distance was found to be too short to work from across the room. I don't recall whether anybody ever produced a cure, but it seemed it was attributed to the different IR transmitter diode designed into the new machines.

Alan

[rprosperi]

(09-18-2015 02:41 PM)Martin Hepperle Wrote:  Well, the HP-49 has some difficulties with IR ... it does not have IR Leds! There is a serial interface only.

Well, at least I didn't recall the 49's IR characteristics for a very good reason...

And another reason to not like the 49 very much.

Thanks Martin.

[Katie Wasserman]

I just tried a few tests of the 50g and the 82240B printer. From what I can tell the calculator to printer distance is so very short becasue they are not using the same carrier frequency. The 82240B wants a 38KHz carrier but the 50g is generating a 32KHz carrier (I measured this). This can be remedied by using a 33KHz receiver (a little off still, but much closer) like the TSOP38233 and modulating an IR emitter at a carrier frequency of 38KHz. Pretty easily done, with something as simple as a 555 chip.

I don't have any 33KHz receivers at the moment, but I'll do some more playing around to try to confirm this hypothesis.

[followup]

So, I made a little repeater using a TSOP38238 IR receiver (this one is for 38KHz but has a pretty wide bandwidth) and a 555 timer to get close to a 38KHz modulation frequency and I can get a range of better than 30 cm from the calculator to the IR receiver and a good range from the IR emitter to the printer depending on how much power is used. I'm sure that I'd get a better range form the calculator to the IR receiver using the TSOP38233 (desinged for 33KHz)

However, a 555 timer with RC components is not a good choice for this project as the frequency will drift with voltage and temperature. A crystal or ceramic resonator would be a better choice. Also, you need to be careful to isolate the IR receiver from the IR emitter or it will feedback -- I had this problem at first.

Instead of reinventing the wheel here and given that: (1) almost all modern IR receivers seem to be more sensitive than the one built into the 82440B and (2) the need to isolate the IR receiver form the IR emitter. I suggest that buying almost any commercial wired IR extender will do the trick almost as well as a custom solution.

[Sukiari]

Thanks all for your suggestions.

[Dave Shaffer]

As I understand Katie’s approach, she is demodulating the calculator signal with the TSOP38238, and then remodulating another LED with the 555 oscillator (gating the 555 with the output from the TSOP chip).

As an alternative, here’s a fairly simple circuit that actually repeats the individual light pulses, with a potentially strong (bright) LED acting as the signal transmitter. This should allow you to extend the range of your HP 50G IR output. Just park your calculator so its output IR signal shines on the detector diode of this circuit and fire away. The output diode blinks in synchronism (at the microsecond level) with the calculator IR signal and if it is bright enough, should allow it to be some moderate distance from the printer. This will not help the mismatch between carrier frequencies which Katie alluded to, so the improvement may actually be marginal.



The circuit uses a QSD2030 photodiode detector sensitive to visible and infrared light, which has an intrinsic very fast response time: 10 nanosec. For the simple circuit here, the response time is rather longer, around a microsecond, set (I think) by the time constant of the diode capacitance and resistor R1. If R1 is bigger, the circuit is more sensitive to light but the response time gets longer, too. The angular cone of sensitivity of the diode is rather small, centered along an axis down through the top of the diode plastic case, so you do have to aim the calculator accurately.

The photocurrent across R1 raises the voltage on the negative input pin of the LM339, which is a fast comparator (response time of around a microsecond here). When the voltage on the negative input exceeds the voltage on the positive input (set by the R2 - R3 voltage divider), the comparator changes output state and turns the LED on. For more sensitivity, the value of R3 can be lowered so that the voltage input on the negative pin needs to rise to a lower value before the LED turns on. At some point, though, a noise threshold will be reached. Also, the QSD2030 may need to be shielded from stray light to achieve the desired sensitivity.

The LM339 is rated to sink up to about 16 mA. If more current is needed to drive your desired IR “transmitter” LED, the LM339 can be used to drive a transistor switch.

I have tried this with only a visible light output LED (so I can see what’s happening!), but it should work with just about any LED. Just make sure your power source can supply the necessary current, and adjust R4 accordingly. R5 is an empirical addition, which assures the LED turns off rapidly. Somebody who understands circuits better than I do can probably suggest a better way to control the LED. Here, the LED (or at least the voltage across it measured with an oscilloscope) turns on and off in a microsecond or so - plenty fast enough to emulate the calculator LED transmitter.

To duplicate this circuit should not be costly - my major expenses were the QSD2030 and LM339, both available for under $1 each (neglecting shipping; see Ebay and/or digikey). The rest of the components I had lying around (as any ham radio operator with a reasonable “junk box” would have!).

I have verified that the circuit responds to a 48SX that I borrowed (whose output pulse frequency is very close to 33 kHz).