troubleshooting a cash drawer solenoid - really... justification for a SCOPE!!! - Page 1
Forum section: electronics / beginners

author: rutgrad
author_rank: Newbie
timestamp: July 25, 2016, 02:12:21 pm
content: Hello, I am a long time "lurker" in the forums and finally have an opportunity to put some of the knowledge I have gained from the forum and videos to work. I just ordered my DSO1054Z for this project. Finally have a reason and purpose to acquire my own scopeSo here is my challenge... a point of sale (POS) system uses an Epson receipt printer (TM-T88IV). The printer has an RJ11 cash drawer trigger port which sends a 24V pulse to activate a solenoid which mechanically opens a cash drawer. I have tried multiple cash drawers and multiple cables and cash drawer operation is not triggering. So I figured I would create a breakout cable to test to see whether I am getting any signal, bad signal or incorrect voltage, but I don't want to blow up my new scope when it arrives. I also I want to make sure my test protocols are correct.The RJ11 port is configured as follows: (I have also included a detailed pdf of the circuit and details of its operation)Pin1: Frame GNDPin2: Drawer Kick-out signal1 (Output)Pin3 Drawer Closed / open signal (input) "provides drawer state"Pin4: +24VPin5: Drawer Kickout drive signal 2 (Output) "for second cash drawer if required"Pin6: Signal GNDI presume I should probe pin 4 to make sure it has +24V. Then probe pin Pin 2 looking for 24V when open signal is sent.signal should last according to the following calculation found in teh atacehd PDF (2mS x t1) where t1 is set to 100mS in our softwareI assume i have to set the scope to trigger so the "capture" occurs. not sure how to do that but I will certainly try and RTFM when it arrives. (if I can avoid the urge to probe!)Sound about right? Any advice would be greatly appreciated.

author: pyroesp
author_rank: Regular Contributor
timestamp: July 25, 2016, 04:53:39 pm
content: All (?) scopes come with a little square wave gen of 1kHz. Connect your probe to it and have a play with that (triggering correctly , single shot, continuous, etc) just to have a feel for the scope. Also, there's a tutorial here on how to use a scope, might be interesting to read:Oscilloscope training class (long)Also, set your probe to x10 and configure the channel to using a x10 probe (if it's one of those x1 - x10 probes).I don't see the pdf on your post ?Down-right, there's the 1kHz sq. wave on the rigol DS1052E.

author: CJay
author_rank: Super Contributor
timestamp: July 25, 2016, 09:04:27 pm
content: Nice reason to buy a 'scope but while you're at it, order some capacitors for the TM88 power supply, they go leaky nd cause exactly that problem.

author: rutgrad
author_rank: Newbie
timestamp: July 25, 2016, 11:12:46 pm
content: Thanks for your replies. FYI... I modified my original post to add the missing document. Apparently it was just a tad too large first time.

author: SL4P
author_rank: Super Contributor
timestamp: July 26, 2016, 08:50:32 am
content: I think you're working under an incorrect assumption.The cash drawer does NOT output a 24V pulse.On page 1 of the PDF manual, it clearly indicates an open collector arrangement, and a 24V supply for the drawer solenoid.Put the high side side of the solenoid to the 24V rail, and (assuming the solenoid is within the open-collector rating), put the low side of the solenoid on the drawer output pin.Remember to put a diode across the solenoid to catch EMF kickback.

author: PA4TIM
author_rank: Super Contributor
timestamp: July 26, 2016, 09:33:11 am
content: And then you can use your scope to test the psu for ripple to check if the caps are OK