Filter msg using trigger node, to only receive one.
e.g.
[{"id":"dfed8e71.e5e8c8","type":"trigger","z":"5a245aa1.510164","name":"","op1":"","op2":"","op1type":"nul","op2type":"pay","duration":"250","extend":true,"overrideDelay":false,"units":"ms","reset":"","bytopic":"all","topic":"topic","outputs":1,"x":360,"y":1760,"wires":[["3f35d274.99189e"]]},{"id":"cda23beb.ee4ea","type":"split","z":"5a245aa1.510164","name":"simulate 7 msg","splt":"\\n","spltType":"str","arraySplt":1,"arraySpltType":"len","stream":false,"addname":"","x":390,"y":1700,"wires":[["dfed8e71.e5e8c8"]]},{"id":"3f35d274.99189e","type":"debug","z":"5a245aa1.510164","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":620,"y":1760,"wires":[]},{"id":"7e3a17af.07e5","type":"inject","z":"5a245aa1.510164","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"[1,1,1,1,1,1,1]","payloadType":"json","x":150,"y":1680,"wires":[["cda23beb.ee4ea"]]}]