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Re: 12 v high side switch - need advice

 by Dave Mueller ¦  Sat Dec 10, 2016 7:52 pm ¦  Forum: Projects ¦  Topic: 12 v high side switch - need advice ¦  Replies: 2 ¦  Views: 624

Bipolar transistors (the common PNP and NPN types) are controlled by current, not voltage. If you want to turn one on or off with a microcontroller or other logic chip, you must put a resistor in series with the base. The actual value depends on the characteristics of the transistor and the load cur...

Re: RS-485 Breakout Board

 by Dave Mueller ¦  Sat Nov 12, 2016 8:10 am ¦  Forum: SparkFun Product Questions ¦  Topic: RS-485 Breakout Board ¦  Replies: 1 ¦  Views: 406

RTS is used to enable the transmitter and disable the receiver and vice versa. This is required since all devices are on the same pair of wires, the protocol is half duplex.

Re: STA540 Input Attenuation Help

 by Dave Mueller ¦  Thu May 05, 2016 5:14 pm ¦  Forum: SparkFun Product Questions ¦  Topic: STA540 Input Attenuation Help ¦  Replies: 1 ¦  Views: 394

My guess is something else is wrong. With the pots turned to the lower limit, the inputs to the STA540 are grounded. Read the product comments, I think there were issues with the thumping that turned out to be power supply related.


Re: Datasheet Humor

 by Dave Mueller ¦  Wed Feb 24, 2016 7:09 pm ¦  Forum: Forum ¦  Topic: Datasheet Humor ¦  Replies: 3 ¦  Views: 3191

A long time ago, I came across a web page full of real "fake" IC and transistor data sheets, many from TI.
And for the ultimate, Google the Rockwell Retro Encabulator.


Re: Need help finding a rain sensor

 by Dave Mueller ¦  Sun Jan 31, 2016 5:38 am ¦  Forum: Projects ¦  Topic: Need help finding a rain sensor ¦  Replies: 5 ¦  Views: 614

Most rain buckets I've looked at are in the $50 to $100 range. Get one with a cable to the display, I think most of them just pass the contact closure to the display.

Re: serial to USB, NOT USB to serial

 by Dave Mueller ¦  Sun Jan 31, 2016 5:36 am ¦  Forum: Projects ¦  Topic: serial to USB, NOT USB to serial ¦  Replies: 6 ¦  Views: 680

Ditto on the Raspberry Pi. There's a utility called socat that allows you to link two serial ports. You'll need a USB/RS232 adapter as well. Save yourself some grief and get a genuine FTDI adapter from Mouser or Digikey for $15. About 10 minutes worth of work :-)


Re: 3 watt Led draw vs Femtobuck output

 by Dave Mueller ¦  Wed Dec 09, 2015 7:31 pm ¦  Forum: SparkFun Product Questions ¦  Topic: 3 watt Led draw vs Femtobuck output ¦  Replies: 3 ¦  Views: 350

LEDs are current controlled devices. The Femtobuck is a "current source", designed to provide 350 mA to any load (within reason). If you connect it to the 3 W led, the voltage across the led will be slightly less than the 3.2-3.8 V range. If you changed the "programming" resistor on the Femtobuck so...

Re: Non-Invasive Current Sensor - 30A

 by Dave Mueller ¦  Wed Oct 28, 2015 6:12 pm ¦  Forum: Forum ¦  Topic: Non-Invasive Current Sensor - 30A ¦  Replies: 5 ¦  Views: 4176

Put the sensor on the circulating pump (I'm assuming there is one in the loop) or any other 120/240VAC device in the system that will draw current while heating.

Improving range of BC127 Bluetooth Audio Breakout

 by Dave Mueller ¦  Wed Oct 28, 2015 5:16 pm ¦  Forum: SparkFun Product Questions ¦  Topic: Improving range of BC127 Bluetooth Audio Breakout ¦  Replies: 0 ¦  Views: 183

I've found the range of the BC127 to be somewhat disappointing. I'm using a cheap BT speaker to stream audio, at best I'm getting 15 feet away before the audio stream starts to break up. With the same speaker and my Nexus tablet, I can be 2 rooms away and still have a good link. I read in the BlueCr...

Re: Using a peltier (TEC) to keep cell phone ambient temp

 by Dave Mueller ¦  Sat Jun 20, 2015 8:38 am ¦  Forum: Projects ¦  Topic: Using a peltier (TEC) to keep cell phone ambient temp ¦  Replies: 9 ¦  Views: 627

Put it in a small cooler. Leave the lid off while you drive to work so it's more or less ambient temp inside the cooler when you get to work. Put the phone in, put the lid on. That should at least slow down the temperature rise the phone sees.

SFE Pint Glass!

 by Dave Mueller ¦  Fri May 29, 2015 5:15 pm ¦  Forum: New Product Ideas ¦  Topic: SFE Pint Glass! ¦  Replies: 0 ¦  Views: 1110

I noticed one in the latest caption contest. Stop holding out!

Re: Hey guys, starting out and need a pointer!

 by Dave Mueller ¦  Tue Apr 21, 2015 4:50 pm ¦  Forum: Projects ¦  Topic: Hey guys, starting out and need a pointer! ¦  Replies: 7 ¦  Views: 509



Re: Counterfiet Parts

 by Dave Mueller ¦  Mon Mar 23, 2015 4:29 pm ¦  Forum: Forum ¦  Topic: Counterfiet Parts ¦  Replies: 5 ¦  Views: 2122

It took a few days to figure out the word I was looking for... Dastardly.

Re: Redboard ISP Programmer pin direction

 by Dave Mueller ¦  Sat Mar 21, 2015 7:44 am ¦  Forum: Arduino ¦  Topic: Redboard ISP Programmer pin direction ¦  Replies: 2 ¦  Views: 689

I believe he's talking about the Redboard not being labelled.

It is, but it's hard to see. There's a small vertical line next to pin 1 on the silkscreen. Check the photo for the retired version:

Re: Counterfiet Parts

 by Dave Mueller ¦  Sat Mar 21, 2015 7:41 am ¦  Forum: Forum ¦  Topic: Counterfiet Parts ¦  Replies: 5 ¦  Views: 2122

Wow, that's just...

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