I hardly don’t know anything about electronics, just a developer. I bought a K8055, and reading from an LDR or temp-resistor works fine.
The problem: I want to use a DigitalOutputChannel to switch a relay, and I cannot get it working. I read some formumsand stared at the drawing in the PDF, but this is what happens:
I interpreted the manual and the forum-posts I read as following:
I have a 5V DC adapter.
I have a relay that switches at 5V. I used my multimeter to measure the resitance, which is about 80 Ohm. When I create the following:
Adaptor+ -> Multimeter -> Relay -> Adaptor-
The relay switches, and I see a small current running, which certainly does not exceed the current that the ULN2803 can switch (about 0,06amps which is correct regarding 5/80…)
I think I should connect the Adaptor+ to CLAMP and the Adaptor- to GND. When I do this, a current of 200mA is running through the ULN2803, which gets pretty warm already. But it’s 5 * 0.2 = 1 Watt, right? So no problem.
When I connect the relay to CLAMP and for instance DigitalOutputChannel2, everything works: I can switch the relay. The current fluctuates beteen 0.18A to 0.24A. However, the ULN2803 gets pretty warm.
When I do the same as 4, but then with DigitalOutputChannel1, something strange happens: when I use the software to switch DigitalOutputChannel1, the relay switches, but then I measure a current of 0.6A and the ULN2803 gets bloody hot! When I switch of the DigitalOutputChannel, this current keeps running, until I disconnect the 5V adaptor.
As I wrote, I read the manual. But the problem is that I obviously do not understand the drawing at page 19. I looked up some sites dat explain the icons, but some of the components drawn on page 19 I cannot find.
So that’s why I tried to describe how I connected it, asking the question what I’m doing wrong.
I am having the same issue but I am not as far yet as I am waiting for an answer before hooking things up. When I say answer I mean something other then read page 19…ok guys I have stared at this page forever now. I understand the hookup but it is somewhat vague. it says do not use a power source greater then .1 A, but that is dependant on what the K8055 pulls or rather the ULN2803. The ULN2803 has a switching max of .5 amps so it is to assume you are putting it on a board that does not pull more than then this and thus all woul be fine. If K8055 pulls .6A you can damage the ULN2803 it seems.
casperdegeus,
something is very wrong with your hardware if you are getting .6A draw from out1 through ULN2803 I see why it would be hot. The .15 to .2 seems ok, surprised it warm but maybe that is normal. Be good for velleman to comment on that.
I have not tested the hookup yet as I am waiting to hear from support before attaching a wall adapter in even though I understand it all technically. Are you saying that you got out2 to work? so all is well with all lines but out1? If out1 pulls .6A it is probably the freezing issue you have with the line not turning off unless clamp power is cut. Almost sounds like out1 has an issue or rather an issue when going through ULN2803. …curious what do you read Voltage wise from line 1 before going through ULN2803? Have you switched the same chip from the other side of the board to see if line one inside ULN2803 is ok? I would do this after you feel all lines work but this one…maybe its the 2803 IC?
I actually posed the question about using the 5V from the board to clamp cause when you only need TTL 5V. If this works, it would completely eliminate the need for an external source? …still waiting on an answer
The external “open collector” design is nice cause you can switch things other then LEDs and TTL inputs for controls and relay boards, but would be nice if you could just get a good 5V TTL from the outputs in a simplier way. I have an idea to do this, but rather use what is there and not mod it.
I am probably ok to test the suggested hookup with my AC/DC adapter which is 5V 1A …but I rather wait for an answer even more so after reading your post as I am now concerned that ULN2803 might pull more then .5 amp from may wall adater and start damaging things.
hopefull velleman support supplies some insight for us and how much we can expect ULN2803 to pull when a outline is triggered + is we can just harness the onbaord 5V to clamp for TTL 5V.
Hi, please find some comments embedded in your text below.
[quote=“casperdegeus”]
I have a 5V DC adapter.
I have a relay that switches at 5V. I used my multimeter to measure the resitance, which is about 80 Ohm. [color=red]OK[/color]
When I create the following:
Adaptor+ -> Multimeter -> Relay -> Adaptor-
The relay switches, and I see a small current running, which certainly does not exceed the current that the ULN2803 can switch (about 0,06amps which is correct regarding 5/80…) [color=red]OK[/color]
I think I should connect the Adaptor+ to CLAMP and the Adaptor- to GND. [color=red]Indeed.[/color]
When I do this, a current of 200mA is running through the ULN2803 [color=red]Where do you exactly measure that current?[/color]
, which gets pretty warm already.
[color=red][b]This is not normal. Only connecting an adapter between Clamp and GND should not send any current through the ULN.
Possible reasons:
the clamping diode(s) in the ULN have been destroyed while an output is “0”. (the destruction will happen if driving relays without connecting “clamp” to the + of the adapter)
the polarity of the adapter is wrong.[/b][/color]
[color=red]You should solve this problem first before going any further.[/color]
But it’s 5 * 0.2 = 1 Watt, right? So no problem. [color=red]It is. (see above)[/color]
When I connect the relay to CLAMP and for instance DigitalOutputChannel2, everything works: I can switch the relay. The current fluctuates beteen 0.18A to 0.24A.
However, the ULN2803 gets pretty warm. [color=red]not normal, see above…[/color]
Hi, After studying the circuit diagram, some comments (in red):
[quote=“kyleg”]I am having the same issue but I am not as far yet as I am waiting for an answer before hooking things up. When I say answer I mean something other then read page 19…ok guys I have stared at this page forever now. I understand the hookup but it is somewhat vague. it says do not use a power source greater then .1 A, but that is dependant on what the K8055 pulls or rather the ULN2803. [color=red]The external power supply is only for the items connected to the “digital output”. The board itself is powered via USB.[/color]
The ULN2803 has a switching max of .5 amps so it is to assume you are putting it on a board that does not pull more than then this and thus all woul be fine. If K8055 pulls .6A you can damage the ULN2803 it seems.
[color=red]The power that the external source can deliver is not so important, it can be more than 0.1A without any problem. The current through the ULN is limited by the resistance of the items connected to the digital output and the voltage of the external power (e.g. 5V / 80 ohm = 62.5 mA – see example of casperdegeus --).[/color]
casperdegeus,
something is very wrong with your hardware if you are getting .6A draw from out1 through ULN2803 I see why it would be hot. The .15 to .2 seems ok, surprised it warm but maybe that is normal. Be good for velleman to comment on that. [color=red]When only the external power supply is connected to Clamp and ground the ULN should stay cold. [/color]
I am probably ok to test the suggested hookup with my AC/DC adapter which is 5V 1A …but I rather wait for an answer even more so after reading your post as I am now concerned that ULN2803 might pull more then .5 amp from may wall adater and start damaging things.
[color=red]Should be no problem (see earlier comment).[/color]
hopefull velleman support supplies some insight for us and how much we can expect ULN2803 to pull when a outline is triggered + is we can just harness the onbaord 5V to clamp for TTL 5V.[/quote]
Thanks so much for your help! I just read both stories, and this really helped.
After reading the two posts, I switched both ULN2803’s, and now the relay-switching works! I probably damaged the ULN by connecting things wrong in the first place, but my lack of experience didn’t make me think it was damaged since the ULN still was doing someting.
Anyway, I am going to try and find a new ULN2803.
Thanks so much again for your help guys, this is great!
Hi, To my opinion the circuit diagram on page 19 is clear (but I am an electronics engineer). So, the problem is here indeed the capability to read and understand circuit diagrams (without throwing any stones of course).
Thanks for your comment Dany. It is nice to see that people help eachother out. This is the main purpose of this forum. I wrongfully assumed that people that build level 5 kits are able to read a schematic diagram. Apparantly, I was wrong. Maybe we can add a detailed, less technical drawing on how to connect a relay…
Thanks for the replies. I don’t think page 19th is confusing in regards to the symbles, but rather different configuration setups. It assumes you only want to use a external powersupply for a relay or other that is to be directly connected to the K8055. The only thing that is confusing is how to use the K8055 5V power directly for TTL to a controller or 5V relay. My confusion was that I did not know what ULN2803 did in the circuit, but now I do. It (and correct me if I am wrong) provides the ground line of clamp so that you can utilize higher current then the board.
Like I said I think it is very cool that the “open collector” feature is on this board and but I was expecting outs to yield 5V TTL signals out like phidgets and other I/O boards…but no biggy I found a fix or actually a modification that I test that works.
Basically I see 4 ways to utilize the Digital outputs of this board. I actually took some pictures last night so maybe I will post a link to them posted on my site.
4 ways:
Use the board design as is and use an external power supply for your switching current (PSupply to clamp and ground and Output line to negative end of the relay’s switch pin.
Use a relay or motor controller board that accepts TTL inout for switching. Here in stead add the ground of K8055 PSupply to ground of Relay or Motor controller board and Output line to TTL in of board (5V limit! in the powersupply you are using here.) This is for switching the boards and does not account for extra power that a motor controller may have to power the motor. Now what happens here is if you switch “on” the outputline, you shut off your relay or motorcontroller board…so it works for a single line. But if you have a duel or quad relay board or duel motor controller board forget it! its all off or on when in fact you may want one off and one on seperately…hence the need for TTL switching.
Do not add relays and LEDs to the outputs of the K8055 that you want to supply CMOS or TTL logic. In this scenerio, we will not be using them as collectors. Reserve these on your board instead to provide 5V (logic CMOS TTL) to a relay or motor controller that is looking for this signal. Move the green connector/s back 1 space on the board to the spot where the LED was going into go. Connect instead a jumper from the the spot where the resister for this LED was going to and solder it to the pin of the green screw connector. Connect ground of K8055 to ground of controller. Get a jumper cable for K8055’s own 5V+ power (upper pin on SK2 and SK3) and connect this 5V+ of the K8055 to the logic power of the relay or motor controller. Connect your modified output (which now sends 5V) to TTL input line on controller and your all set.
I usually just use the I/O board’s 5V+ power for powering the logic of any relay boards or motor controller boards, But now have the need to keep the realy baord 20 feet away and send the input through a line RCA cable. in this case K8055 ground and 5V TTL go through one cable (2 wires) and then the Relay switch gets its own power from a 5V AC adapter. Kind of a weird setup, but works out if your K8055 is to be seperated from the thing your switching.
PWM TTL is different I have not realy come up with a mod for that but suspect it is the same concept.
If these setups are confusing let me know and I can post some picts. Also the MIDAS K8055 manual has tons of circuit setups for K8055 as well. MIDAS for those that do not now is the Director Plugin for K8055 but their server is down till Oct. 08. If you want the manual post an email and I’ll send.
Hiya Kyle,
This is many years after your post, but if you can send me a copy of the MIDAS k8055 manual, that would be great!
I could do with looking at the wiring diagrams…
It’s no longer available via Google…
Thanks
Lawrence
