Having some problems with basic C++ / Arduino typecasting… I think. I’m playing with the Nightshade energyShield and trying to Spark.publish() a sprintf’d JSON string but the numbers are getting messed up, and I can’t figure out whether it’s the Wire() not working or if it is a sprintf typecasting …

[image] emc2: {"data":"{"mV": 9993, "mA": 5118, "percent": 127.500, "temp": 255.875, "","ttl":"60","published_at":"2014-11-17T04:42:21.680Z","coreid":"xxxxx"} Hi @emc2 Looks like you are running into the 63 character limit for Spark publish. You can make your fields names shorter and gain s…

Unfortunately it doesn’t appear to be the old 63-char limit this time. That publish response was the entire listener object from the cloud. I just tried reducing the publish char variable down to 64 bytes, and now am only publishing this: sprintf(publishString,"{\"mV\": %i}",Voltage); Spark.publi…

@emc2 , it might be a silly question, but have you tried to Serial.println(publishString); to see if it’s a sprintf or a Spark.publish problem?

sprintf() doesn’t do type casts and cannot. [Technical reason: the printf family use varargs, the va_list contains no variable type information.]. You are printing Percent, declared int, using a float format %3.3f. You must explicitly do the cast yourself, printing (float)Percent/200.0. Similarly …

The strange values might (=won’t) be a side effect of exceeding the 63 char limit: Why would Spark.publish() screw up the part of the text that contains the numbers and not corrupt the part of the text that contains the variable names? (=!) No the damage happened earlier, before Spark.publish() was …

Hi @emc2 You are definitely hitting the limit since (1) I counted them out (the double-quotes are funny when you count since they are escaped) and (2) the entire “Vadp” parameter is missing in your result. It sounds like you are having other problems too. As others have said, sprintf can’t cast–it…

@emc2 I am having the same issue. It is not you. When I power my spark core via the USB and read the serial output from NightShade’s RealAll example, I get perfectly good measurements. Note that I only have lines running from the SparkCore for GND, D0 and D1. The Core is essentially powered from…

Originally, I did end up hitting the Spark.publish() character limit, but as you have noticed that was a separate problem. I now think that this problem is related to the Shield shield and the communication pins that the energyShield uses. Page 7 of the energyShield Product Manual outlines the two …

Side note - I was testing the energyShield on an Uno R3, and THAT is where the Serial.print() results worked properly. I have NOT been able to get the communication to work at all with the Spark Shield shield, at all.

Looking like it might be Shield Shield and the TI Logic Level converter used to raise the voltage to 5V. [image] I2C on Shield Shield Hardware I think I2C on the shield shield has some issues based on past forum post. Let’s t…

Serial.print() vs sprintf() and typecasting

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cloris November 24, 2014, 1:04pm 12

Looking like it might be Shield Shield and the TI Logic Level converter used to raise the voltage to 5V.

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Serial.print() vs sprintf() and typecasting

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