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Seven segment led scoreboard

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sparky72

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First of all, let me say that I am not an university student nor an electronics engineer but just a retired senior citizen that is enjoying this new found hobby of mine. Last winter I built a seven segment led scoreboard using a multiplexing circuit, with a great deal of help from k7elp60 at this site. This year I would like to enhance the scoreboard by replacing the momentary switches that control the digital display with an RF remote control system if possible. The remote system that I have been looking is the TWS-434A transmitter & RWS-434 receiver system located at RF Remote Control .My question is, would there be too much interference coming from the multiplexing to let this RF system work? Also if the system will work would it be possible to use, say a 2N2907 PNP transistor as a switch in place of a relay, since I am only switching off and on at most 400mah? Thanks in advance for any info that I may receive.
 

mneary

New Member
When you ask for 2N2907 you'll probably get a PN2907A unless it's another senior citizen like me. Just beware that the PN2907A only has a saturated HFE of about 10 in the 500 mA region. (I assume you mean mA and not mah).
 

sparky72

Member
seven segment scoreboard

When you ask for 2N2907 you'll probably get a PN2907A unless it's another senior citizen like me. Just beware that the PN2907A only has a saturated HFE of about 10 in the 500 mA region. (I assume you mean mA and not mah).


Thanks Mneary for your response. I stand to be corrected. It should be mA and not mah. According to the Philips data sheet for the 2N2907A the min hfe is 100, and the collector current max is -600 mA. I am not sure if this will handle switching or, even if the multiplexing circuit will interfere with the RF remote switching I would like to use. I guess maybe I should just use a switching relay instead. Any comments that you may have in this regard would be appreciated.
 

mneary

New Member
The collector current max of 600 mA is listed under "Limiting Values". They are not normal operating conditions.

The gain is specified with -10V applied to Vce, which at 600 mA is 6 watts. Test conditions for this figure are for 300 microseconds. Note that if you plan to use a PNP as a switch, this configuration would be losing as much as 10V in the switching process.
 
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