dirknerkle
Supporting Member
I was noodling some ideas about making a super-cheap DC SSR and came up with this idea...
The concept uses an ULN2804A as the driver. It can handle up to 50volts which seems to take care of most things we do with DC and LEDs -- at least single LEDs and some strips. Each of the eight output pins can handle 500ma continuous current; peaks up to 600ma. And you can use two or more outputs together to multiply the current capability.
Also, using header pins and Dupont connection wires would provide selectivity with the input channels to the ULN2804A, and on the output side of the chip, the assignment of the desired channels to the terminal blocks (lights). Selectivity might be helpful in cases where one output was overloaded or shorted, killing that output on the chip; simply set the Dupont wire to a different input on the ULN and the terminal block to the same respective output. In a pinch, the ULN2804 could be replaced with a ULN2803, ULN2802 or ULN2801 if need be, but the 2804 can carry more juice.
The RJ45 jack would be pinned for normal DIY 4-channel SSR use with +5v on pin 1, pins 2-4-6-8 for the channels and pin 7 ground, back to the controller. Since the ULN2804 inverts the polarity (+v input results in -V output), you'd want to take that into consideration in your wiring.
Tayda's current pricing for this design:
ULN2804 $.81
RJ45 jack $1.60
2-conductor terminal blocks are either $.12 or $.15 each (total $.72 - $.90)
1 40-pin single row of breakapart headers is $.15
18-pin DIP socket is $.06
A pack of 40 200mm jumper wires is $.90
It looks like you could build this thing for under $5 and you'd have parts left over. This could be super-compact, too and if you wired it directly instead of using header pins, jumper wires, and terminal blocks, it could be like an extension of the cat5 cable and be cheaper yet!
And if you're wondering, no, I don't plan on having PCBs made for this. The postage to send it out would be about 40x more than the cost of the PCB. You could easily put this together on a piece of cardboard or tagboard - punch holes with a nail, fit the parts in, solder it on the bottom side and you're good to go.
The concept uses an ULN2804A as the driver. It can handle up to 50volts which seems to take care of most things we do with DC and LEDs -- at least single LEDs and some strips. Each of the eight output pins can handle 500ma continuous current; peaks up to 600ma. And you can use two or more outputs together to multiply the current capability.
Also, using header pins and Dupont connection wires would provide selectivity with the input channels to the ULN2804A, and on the output side of the chip, the assignment of the desired channels to the terminal blocks (lights). Selectivity might be helpful in cases where one output was overloaded or shorted, killing that output on the chip; simply set the Dupont wire to a different input on the ULN and the terminal block to the same respective output. In a pinch, the ULN2804 could be replaced with a ULN2803, ULN2802 or ULN2801 if need be, but the 2804 can carry more juice.
The RJ45 jack would be pinned for normal DIY 4-channel SSR use with +5v on pin 1, pins 2-4-6-8 for the channels and pin 7 ground, back to the controller. Since the ULN2804 inverts the polarity (+v input results in -V output), you'd want to take that into consideration in your wiring.
Tayda's current pricing for this design:
ULN2804 $.81
RJ45 jack $1.60
2-conductor terminal blocks are either $.12 or $.15 each (total $.72 - $.90)
1 40-pin single row of breakapart headers is $.15
18-pin DIP socket is $.06
A pack of 40 200mm jumper wires is $.90
It looks like you could build this thing for under $5 and you'd have parts left over. This could be super-compact, too and if you wired it directly instead of using header pins, jumper wires, and terminal blocks, it could be like an extension of the cat5 cable and be cheaper yet!
And if you're wondering, no, I don't plan on having PCBs made for this. The postage to send it out would be about 40x more than the cost of the PCB. You could easily put this together on a piece of cardboard or tagboard - punch holes with a nail, fit the parts in, solder it on the bottom side and you're good to go.