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I'm just a beginner and need some assistance. below is a diagram of a 4CH reciever which works fine with some leds and it reports 5V positive on Data0 when holding channel 0 on the transmitter. What's not working is when attempting to use a 5V DC relay as shown in diagram, the relay clicks and seems to work fine with a direct input.

I'm using USB Powered socket which is 5V DC 0.5A I believe. I'm really puzzled while its not working.

schematic

SUGGESTED

schematic

simulate this circuit – Schematic created using CircuitLab

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The relay draws more current than that module can supply. If you keep doing such tests you may damage the receiver!

If you read the SC2272-M4 datasheet, you'll see it can supply a maximum current of 3 mA. That relay needs 89 mA at a 55 ohms coil resistance. So the load current is 5 / 55 = 0.09 A = 90 mA. Now, the minimum hFE of the transistor should be (0.09 / 0.003) x 5 = 150. The resistor between receiver and transistor base should be 0.2 x 55 x 150 = 1650 ohms. Choose 1.8 k. Calculations made on http://pcbheaven.com/wikipages/Transistor_Circuits/

Due to the very low available current from receiver output pin, a high hFE transistor is required. 2N2222 should work (its maximum hFE is 300).

Use a (transistor) driver. Something like:

enter image description here

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  • \$\begingroup\$ Ya I thought it could be the amps, didn't relise I could break it through.. Will need to buy transistor. Additionally, are you recommending 2 power sources, or one but both input on both with more AMPS. \$\endgroup\$ – Simon Hayter Jul 30 '14 at 17:15
  • \$\begingroup\$ I've edited my suggest and added what I believe it is your suggesting.. can you confirm thats right or wrong, with any other improvements, :) \$\endgroup\$ – Simon Hayter Jul 30 '14 at 17:25
  • \$\begingroup\$ Is there any reason why you use the diode between the coil pins? I'm sure this has been asked time and time again on here, if you know a question / answer on here that may help then let me know. thx for all your help. \$\endgroup\$ – Simon Hayter Jul 30 '14 at 17:29
  • \$\begingroup\$ Awesome, I'll read that in a moment. In the meantime I'm ordering the parts which is a 10K resistor, a 2N2222A Transistor... the diode, should any work? \$\endgroup\$ – Simon Hayter Jul 30 '14 at 17:40

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