# Help with some simple circuits. **URL:** \ **Category:** Factual Questions\ **Created:** [December 1, 2005, 8:07pm UTC](https://boards.straightdope.com/t/help-with-some-simple-circuits/333601 "2005-12-01T20:07:17Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![Muad\_Dib](https://avatars.discourse-cdn.com/v4/letter/m/35a633/32.png) [@Muad\_Dib](https://boards.straightdope.com/u/Muad_Dib)\ **Post date:** [December 1, 2005, 8:07pm UTC](https://boards.straightdope.com/t/help-with-some-simple-circuits/333601/1 "2005-12-01T20:07:17Z")
First off, this is not for school. How do I make a simple transmitter and a simple remote controlled device? I need a device, as small as possible, that can transmit a simple frequency that can be adjusted between 5 and 10 MHz. I also need a simple remote controlled switch, with which I can press a button and trigger the device from at least 50 feet. How complicated would such circuits be? Would the remote control be easily set off by other signals? I have a few books that show some very simple transmitters but they do not explain how to measure and set the frequency. ---
**Author:** ![Muad\_Dib](https://avatars.discourse-cdn.com/v4/letter/m/35a633/32.png) [@Muad\_Dib](https://boards.straightdope.com/u/Muad_Dib)\ **Post date:** [December 1, 2005, 8:11pm UTC](https://boards.straightdope.com/t/help-with-some-simple-circuits/333601/2 "2005-12-01T20:11:47Z")
I have seen it said that slavery can not exist for long under capitalism and that the only reason it remained in the south for so long is because they were more of a Feudal society than a Capitalist one. However, I do not see why this is so. If you do not recognize the humanity of another I see no reason why this would be incompatible with and unable to survive under Capitalism. Slaves would be treated much how we treat animals. ---
**Author:** ![Muad\_Dib](https://avatars.discourse-cdn.com/v4/letter/m/35a633/32.png) [@Muad\_Dib](https://boards.straightdope.com/u/Muad_Dib)\ **Post date:** [December 1, 2005, 8:12pm UTC](https://boards.straightdope.com/t/help-with-some-simple-circuits/333601/3 "2005-12-01T20:12:54Z")
> [@Muad'Dib](#): > > I have seen it said that slavery can not exist for long under capitalism and that the only reason it remained in the south for so long is because they were more of a Feudal society than a Capitalist one. > > However, I do not see why this is so. If you do not recognize the humanity of another I see no reason why this would be incompatible with and unable to survive under Capitalism. Slaves would be treated much how we treat animals. Reply != post ---
**Author:** ![mks57](https://avatars.discourse-cdn.com/v4/letter/m/b9bd4f/32.png) [@mks57](https://boards.straightdope.com/u/mks57)\ **Post date:** [December 1, 2005, 8:31pm UTC](https://boards.straightdope.com/t/help-with-some-simple-circuits/333601/4 "2005-12-01T20:31:50Z")
You could use a simple crystal-controlled oscillator for the transmitter. You can find schematics and plans for such devices by googling for QRP (low power) HF (high frequency) CW (continuous wave) transmitters or by looking in amateur radio books like the ARRL handbook. You will need an amateur radio license to legally operate it at any significant power level. You may be able to operate it without a license if you comply with Part 15 of the FCC rules, which specify allowable frequencies and power levels for unlicensed operation. The receiver is more complicated. Reliably detecting an unmodulated carrier can be difficult. Most remote controls modulate the carrier with something simple, like audio-frequency tones. There are off-the-shelf ICs (integrated circuits) that can detect the presence of a tone at a specific frequency. Many people use encoder and decoder ICs designed for DTMF (dual-tone multi-frequency or Touch Tone) signaling in telephone equipment. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [December 1, 2005, 9:09pm UTC](https://boards.straightdope.com/t/help-with-some-simple-circuits/333601/5 "2005-12-01T21:09:25Z")
Here’s a remote control switch project: [http://www.discovercircuits.com/C/control6.htm](http://www.discovercircuits.com/C/control6.htm) Rather than building a transmitter and receiver from scratch, I cannibalize $10 radio remote light switches from the local home improvement store. If you don’t have 110v at the remote site, you need to build a little power supply for the receiver. The things have a range of about 50 feet, and go through walls etc. nicely. ---
**Author:** ![Muad\_Dib](https://avatars.discourse-cdn.com/v4/letter/m/35a633/32.png) [@Muad\_Dib](https://boards.straightdope.com/u/Muad_Dib)\ **Post date:** [December 1, 2005, 9:11pm UTC](https://boards.straightdope.com/t/help-with-some-simple-circuits/333601/6 "2005-12-01T21:11:28Z")
I need the transmiter to be hand held and the size of a car remote. ---
**Author:** ![Muad\_Dib](https://avatars.discourse-cdn.com/v4/letter/m/35a633/32.png) [@Muad\_Dib](https://boards.straightdope.com/u/Muad_Dib)\ **Post date:** [December 1, 2005, 9:12pm UTC](https://boards.straightdope.com/t/help-with-some-simple-circuits/333601/7 "2005-12-01T21:12:34Z")
Also, the reciever must be small, something that could fit in a tennis ball, and be battery powered. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [December 1, 2005, 9:22pm UTC](https://boards.straightdope.com/t/help-with-some-simple-circuits/333601/8 "2005-12-01T21:22:59Z")
> [@Muad'Dib](#): > > I need the transmiter to be hand held and the size of a car remote… > Also, the reciever must be small, something that could fit in a tennis ball, and be battery powered. [This unit](http://www.smarthome.com/2536r1wh.html) could be modified to meet those criteria. It’s too pricey, there are cheaper versions. At worst you’d need to build or buy a little [inverter circuit](http://www.aaroncake.net/circuits/inverter.htm) to power the receiver from 12v. ---
**Author:** ![Muad\_Dib](https://avatars.discourse-cdn.com/v4/letter/m/35a633/32.png) [@Muad\_Dib](https://boards.straightdope.com/u/Muad_Dib)\ **Post date:** [December 1, 2005, 9:37pm UTC](https://boards.straightdope.com/t/help-with-some-simple-circuits/333601/9 "2005-12-01T21:37:47Z")
It does not have to controll anything that powerfull. It is intended to set off a small buzzer as part of a practical joke. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [December 1, 2005, 11:08pm UTC](https://boards.straightdope.com/t/help-with-some-simple-circuits/333601/10 "2005-12-01T23:08:30Z")
> [@Muad'Dib](#): > > Would the remote control be easily set off by other signals? Yes. That’s why all radio transmitter/receiver systems utilize some from of modulation or encoding. FRS radios are pretty cheap nowadays (check eBay). I suppose you could remove the speaker from one radio and replace it with a simple comparator circuit that actuates a buzzer. To make it work, simply press the “call” button on the other radio. ---
**Author:** ![spingears](https://avatars.discourse-cdn.com/v4/letter/s/ebca7d/32.png) [@spingears](https://boards.straightdope.com/u/spingears)\ **Post date:** [December 2, 2005, 3:34am UTC](https://boards.straightdope.com/t/help-with-some-simple-circuits/333601/11 "2005-12-02T03:34:55Z")
> [@Muad'Dib](#): > > Reply != post You made a wrong turn in post 2. Take I-95 South bound.