Help amplifying a tiny current

[CDRIVE]

Ouch, I didn't think the SSR's input Z (440Ω) was that low. Sorry about that!

Chris

 

[hevans1944]

Ouch, I didn't think the SSR's input Z (440Ω) was that low. Sorry about that!

Chris

Typically the SSRs have an LED in an opto-coupler input that needs a current limiting resistor. Sometimes they add an inverse-parallel diode across the LED to protect against reverse polarity. Depending on the minimum control voltage, there may also be a visible LED in series with the opto-coupler LED that lights up to let you know a control voltage has been applied. All this LED stuff requires a couple of volts and a few milliamperes of current to get the SSR output to turn on. Not usually a problem with control outputs that sink or source current because you can wire accordingly... but the 10 kΩ "pull-up" is problematical for directly driving an opto-coupler, and the comparator current sinking capability is a little wimpy too. The two conspire to require that a transistor be added to reliably control either a relay or the chosen SSR. That sucks. For a penny or so more the Asian manufacturer could have included the transistor on the circuit board. Caveat emptor.

 

[CDRIVE]

I would think that paralleling the 10KΩ with a 1KΩ should do the trick and eliminate the need for an NPN driver.

Chris

 

[hevans1944]

I would think that paralleling the 10KΩ with a 1KΩ should do the trick and eliminate the need for an NPN driver.

Chris

It's worth trying. That would only add only six milliamperes to the sink current when DO is low but it would drop Vcc = 6 V down to about 1.8 V when DO is high, (6)(440/1440) = 1.8. That may or may not be enough to reliably turn the opto-isolator on. This is assuming the SSR control inputs are connected between DO and common. I vote to try it. Simple is always better if simple works.

 

[CDRIVE]

Actually the 10KΩ isn't the only sink path between Vcc and DO. There's an LED and series 1KΩ in parallel with it. Personally I would try driving the SSR with the board as is. If the SSR needs more drive current I would jump the LED. This would provide a source resistance of 909Ω. With the SSR connected between GND and DO the LED would be a nuisance anyway. This is because it would never be off. It would just be brighter when DO is low.

Chris

 

[Avondale]

been tweaking around with other projects, but i now have all the parts for this, apart from the AA batteries lol
http://imgur.com/PWHa4Dn
here's all the pieces, just need to add some wires!
(did a little testing with these SSR's, theyre a little unintuitive, can't just put a multimeter on them to check that theyre 'on' or 'off', needs a load on them, and maybe a certain type of load to actually let them go 'off' when the 'coil'(not really a coil) current goes off)

further testing and soldering ahead!
but for now check out my other messy creation....
http://imgur.com/zjZRpVo
http://imgur.com/I9fTzl0

 

[(*steve*)]

Yes we probably should have warned you about the characteristics of SSR's

 

[the great potato]

theres a step up board that raises voltage i think was by 4-6 volt on wish.com for cheap maybe something like that might help?

 

[davenn]

theres a step up board that raises voltage i think was by 4-6 volt on wish.com for cheap maybe something like that might help?

but he wants to amplify current not voltage

he hasn't been back for a month or so, so maybe the SSR method worked for him ?

 

[the great potato]

who knows maybe he hooked up a car batt and and a headlight and got his wanted results ! LOL

 

[Avondale]

he hasn't been back for a month or so, so maybe the SSR method worked for him ?

i actually never got this finished, i went off on other projects and decided to come back to it when i am far more knowledgeable about electronics lol
I got some normal relay boards for arduinos, will investigate their use of octocouplers to turn a small current into a larger current!