PCB Connectors

Discussion in 'The Projects Forum' started by rjanish, Jul 12, 2010.

  1. rjanish

    Thread Starter New Member

    Jul 12, 2010
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    I am a physics student building a simple circuit to be used in a research lab, and I having trouble deciding what type to connectors to use in my design. My design will call for 2 signal inputs, 1 power input and 1 signal output on the pcb. I was hoping to mount the pcb inside an aluminum enclosure, on the panel of this enclosure there will be 3 bnc connectors for the incoming and outgoing signal lines, and a connector for a wall-plug ac/dc adapter for power. My plan was then to solder, on the inside of the enclosure, two wires to each of these connectors and hopefully have each pair of wires end inside some sort of nylon connector which would attach to a receptacle mounted on the pcb (smd, preferably). The connectors should be rated for up to 5 amps, and preferable would stand less than 0.75 in vertical when plugged into the board, however this height requirement can be ignored if necessary. I was wondering if anybody here could point me in the right direction to find something that would work for the nylon connector/pcb receptacle combo?
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Have you considered 90° connectors? On these, the pins are inserted in the edge of a PCB, and the ends are bent outwards. That will help you a great deal with the height requirement.

    Are your signals going to be low frequency? If so, you don't have to be terribly particular. However, if you are going to be using higher frequency signals; say >100kHz sine waves or 10kHz square waves, then the impedance becomes more critical. In that case, you might wish to look at using right-angle SMA connectors and semi-rigid coax.

    If your requirements are fairly simple, you may even wish to look at terminal blocks. Terminal blocks are available in a huge variety of current/voltage ratings and configurations. You simply insert the end of a bare wire and turn a screw or flip a cam to secure the connection.
     
  3. rjanish

    Thread Starter New Member

    Jul 12, 2010
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    The 2 inputs are a 2 khz and 100 khz square wave and the output is a 98 khz sine wave
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    OK, with a 100kHz square wave, you'll need at least 1MHz bandwidth or your square wave will start looking quite distorted.

    Please understand that an ideal square wave is composed of the fundamental frequency, plus ALL of the odd harmonics of the fundamental frequency. This implies unlimited bandwidth, which is of course not practical nor possible.

    See this Wiki entry: http://en.wikipedia.org/wiki/Square_wave
    Scroll half-way down, and click the image on the right a couple of times to animate it.

    Matching impedance on both ends becomes critical. Without seeing details about your circuit via schematic representation, it will be very difficult to make decent recommendations.
     
  5. rjanish

    Thread Starter New Member

    Jul 12, 2010
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    I am familiar with the mathematics of square waves. Though, the first thing the circuit does is use a low pass filter to strip off the harmonics and convert those squares to sines waves at the fundamental frequency, so if there's some awkward phase shifting of the higher harmonics by the connector I dont think it would be too big of a deal, as they aren't really being used anyway. I posted a schematic that I made with a free cad program, pcb artist (http://www.4pcb.com/free-pcb-layout-software/).
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    Please post your schematic in .PNG format, resolution of roughly 100-120 DPI.

    That way anyone can view it without having to install any software.

    Installing that software would interfere with my Cadsoft Eagle settings, which I do not wish to compromise.
     
  7. rjanish

    Thread Starter New Member

    Jul 12, 2010
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    I have attached a png version
     
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